Lakhmir Singh Class X Chemistry Chapter 3 – Metals and Non-Metals

Exercise : Solution of Questions on page Number : 131

Answer 1:
Mercury is the metal that exists in liquid state at room temperature. The non-metal that exists in liquid state at room temperature is bromine.

Answer 2:
Metals can form positive ions easily by losing electrons. So, they are called electropositive elements. Non-metals can form negative ions easily by gaining electrons and so, they are called electronegative elements.

Answer 3:
(a) Aluminium is the most abundant metal in the earth’s crust.
(b) Silicon is the most abundant non-metal in the earth’s crust.

Exercise : Solution of Questions on page Number : 132

Answer 4:
Sodium is a metal that has a low melting point.

Answer 5:
Lead is the metal that is the poorest conductor of heat.

Answer 6:
False. Metals react with dilute acids to produce hydrogen gas that burns with a ‘pop’ sound.

Answer 7:
(i) Magnesium reacts with water only on boiling.
(ii) Copper does not react even with steam.

Answer 8:
An iron nail displaces copper from a copper sulphate solution to form a ferrous sulphate solution, due to which the blue colour of the copper sulphate solution fades. Also, copper is deposited on the iron nail, which turns it reddish-brown in colour.

Answer 9:
Aqua-regia is a freshly prepared mixture of one part of concentrated nitric acid and three parts of concentrated hydrochloric acid. Gold and platinum are the special metals that are insoluble in common reagents but dissolve in aqua-regia.

Answer 10:
(a) Carbon dioxide with the formula CO₂ and sulphur dioxide with the formula SO₂ are two acidic oxides.
(b) Sodium oxide with the formula Na₂O and potassium oxide with the formula K₂O are two basic oxides.

Answer 11:
Metal oxides that show basic as well as acidic behaviour are called amphoteric oxides. Aluminium oxide is an example.

Answer 12:
Aluminium and zinc are two metals that form amphoteric oxides.

Answer 13:
When a copper coin is kept immersed in a solution of silver nitrate for some time, the colour of the coin becomes shiny greyish-white due to the deposition of silver on it. The solution turns blue due to the formation of copper nitrate.

Answer 14:
(a) Copper and aluminium are good conductors of heat. This property makes them suitable for making cooking utensils and boilers.
(b) Copper and aluminium are good conductors of electricity. This property makes them suitable for making electric wires.

Answer 15:
(a) Sodium hydride is a metal hydride with the formula NaH.
(b) Hydrogen sulphide is a non-metal hydride with the formula H₂S.

Answer 16:
(a) Gold is the metal that has been placed at the bottom of the reactivity series.
(b) Potassium is the metal that has been placed at the top of the reactivity series.
(c) Mercury is the metal that has been placed just below copper in the reactivity series.

Answer 17:
Of the two metals, copper is more reactive than silver.

Answer 18:
(a) Sodium is a metal that is stored in kerosene oil.
(b) White phosphorus is a non-metal that is stored under water.

Answer 19:
(a) 4Na (s) + O₂ (g) → 2Na₂O (s)
Sodium Oxygen Sodium oxide
(b) 2Mg (s) + O₂ (g) → 2MgO (s)
Magnesium Oxygen Magnesium oxide

Answer 20:
(a) Copper and aluminium are two metals used to make electric wires.
(b) Iron and aluminium are two metals used to make domestic utensils and factory equipment.
(c) Gold and silver are two metals used to make jewellery and to decorate sweets.

Answer 21:
Aluminium metal foil is used to pack some medicine tablets.

Answer 22:
(a) Hydrogen is the non-metal that is used to convert vegetable oil into vegetable ghee (solid fat).
(b) Hydrogen is the non-metal that is used as a rocket fuel (in liquid form).
(c) Carbon is the non-metal that is used to make electrodes of dry cells.
(d) Nitrogen is the non-metal that is used to preserve food materials.
(e) Sulphur is the non-metal that is used in the vulcanisation of rubber.

Answer 23:
(a) Metals are malleable and ductile. That is, metals can be hammered into thin sheets and drawn into thin wires.
(b) Non-metals are brittle, i.e. they break easily.

Answer 24:
Brittleness is the property of being broken easily. Non-metals are the elements that usually show brittleness.

Answer 25:
If a zinc strip is immersed in a solution of copper sulphate, the blue colour of copper sulphate fades due to the formation of colourless zinc sulphate. The metal, copper, reddish-brown in colour is deposited on the zinc strip.
CuSO₄(aq) + Zn(s) → ZnSO₄(aq) + Cu(s)

Answer 26:
If a strip of copper is kept immersed in a solution of silver nitrate, the solution gradually becomes blue due to the formation of copper nitrate and a shiny greyish-white deposit of silver is formed on the copper strip.
2AgNO₃(aq) + Cu(s) →Cu(NO₃)₂(aq) + 2Ag(s).

Answer 27:
When iron nails are put into copper sulphate solution, the blue colour of copper sulphate fades gradually to green due to the formation of ferrous sulphate and the reddish-brown copper metal is deposited on the iron nails.
CuSO₄(aq) + Fe(s) → FeSO₄(aq) + Cu(s).

Answer 28:
When silver is dipped in a copper sulphate solution, no reaction occurs. This means silver cannot displace copper from the copper sulphate solution. Hence, it shows that silver is chemically less reactive than copper.

Answer 29:
When iron fillings are added to copper sulphate solution, iron will displace copper to form iron sulphate. The blue colour of the copper sulphate solution changes to green as iron sulphate is green in colour.

Exercise : Solution of Questions on page Number : 133

Answer 30:
Diamond is a non-metal that has a very high melting point.

Answer 31:
Graphite is a good conductor of electricity and that is why it is used to make electrodes.

Answer 32:
Sulphur and phosphorus are two non-metals that are both brittle and non-ductile.

Answer 33:
Some metals, when exposed to air for a long time, react with oxygen in the atmosphere to form a dull layer of metal oxide on their surfaces. This makes the metals look dull.

Answer 34:
(a) 4Na(s) + O₂(g) → 2Na₂O(s)
(b) Na₂O(s) + H₂O(l) → 2NaOH (aq)
(c) 3Fe(s) + 4H₂O(g) → Red Heat Fe3O₄(s) + 4H₂(g)
(d) Cu(NO₃)₂(aq) + Zn(s) →Zn(NO₃)₂(aq) + Cu(s) (a)(a Zn (s) .

Answer 35:
(a) Magnesium liberates hydrogen gas on reacting with hot boiling water.
(b) The white powder formed when a magnesium ribbon burns in oxygen is magnesium oxide.
(c) Ordinary aluminium strips are not attacked by water because of the presence of a layer of aluminium oxide on the surface of aluminium.
(d) A metal having low melting point is sodium but a non-metal having very high melting point is diamond.
(e) Calcium is a less reactive metal than sodium.

Answer 36:
(a) Metals are malleable, which means that they can be hammered to form thin sheets. For example, gold and silver.
Metals are ductile, which means that they can be stretched to form thin wires. For example, copper and aluminium.
(b) Gold and copper are two metals that are both malleable and ductile.
(c) Malleability is the property of iron that is utilised to produce iron sheets required for to make buckets.
(d) Ductility is the property of copper that is utilised to make thin wires.

Answer 37:
Sodium and potassium are two metals that react violently with cold water.
Three observations when such a metal is dropped in water are:
Reaction is highly exothermic i.e. a huge amount of heat is produced.
Hydrogen gas is evolved in the reaction.
A small explosion takes place because the heat produced in the reaction burns the hydrogen gas. Hydrogen can be identified by the ‘pop’ sound it makes while burning.

Answer 38:
(a) Metal oxides are generally basic in nature, which can turn red litmus solution to blue while non-metal oxides are generally acidic in nature, which can turn blue litmus solution to red. For example, sodium oxide and potassium oxide are metal oxides which are basic in nature; carbon dioxide and sulphur dioxide are non-metal oxides which are acidic in nature.
(b) (i) S and C would yield acidic oxides.
(ii) Na and K would yield basic oxides.
(iii) H would yield neutral oxides.

Answer 39:
(a) Amphoteric oxides are those metal oxides which show basic as well as acidic behaviour. They react with acids as well as bases to form salts and water. Aluminium oxide and zinc oxide are examples.
(b) Acidic oxides: CO₂ and SO₂
Basic oxides: Na₂O and MgO
Neutral oxides: N₂O, CO and H₂O
(c) ZnO and Al₂O₃ are the amphoteric oxides.

Answer 40:
(a) SO₂ is acidic in nature. When it is dissolved in water, sulphurous acid is formed.
Chemical equation: SO₂(g) + H₂O(l) → H₂SO₃(aq)
(b) Na₂O is basic in nature. When it is dissolved in water, sodium hydroxide is formed.
Chemical equation: Na₂O(s) + H₂O(l) → 2NaOH(aq)

Answer 41:
(a) When non-metals react with oxygen, acidic oxides are formed. For example, sulphur on reacting with oxygen form sulphur dioxide. This oxide turns blue litmus solution to red, which shows that it is an acidic oxide.
(b) When metals react with oxygen, basic oxides are formed. For example, sodium on reacting with oxygen form sodium oxide. This oxide turns red litmus solution to blue, which shows that it is a basic oxide.

Answer 42:
(a) Nitric acid is a powerful oxidising agent. So as soon as hydrogen gas is produced due to the action of nitric acid on metals, it oxidises hydrogen to form water and reduces itself to nitrogen oxides. Hence hydrogen gas is not liberated in the reaction.
(b) Magnesium and manganese are two metals that liberate hydrogen gas from very dilute nitric acid.

Answer 43:
(a) Metals generally do not react with hydrogen. But some reactive metals like sodium, potassium, calcium and magnesium can force the hydrogen atom to accept the electrons given by them and form salt-like ionic solid compounds called metal hydrides.
For example:
2Na(s) + H₂(g) → 2NaH(s)
(b) Non-metals react with hydrogen by sharing their electrons with hydrogen electrons to form covalent hydrides.
For example: Sulphur shares its electrons with hydrogen electrons to form hydrogen sulphide that is covalent in nature.
H₂(g) + S(l) → H₂S (g)

Answer 44:
(a) Calcium reacts vigorously with chlorine to form calcium chloride, which is an ionic chloride.
Ca(s) + Cl₂(g) →CaCl₂(s)
(b) When magnesium reacts with very dilute nitric acid, it forms magnesium nitrate and hydrogen gas is evolved.
As the nitric acid is very dilute, it acts as a weak oxidising agent, which is unable to oxidise the hydrogen gas.
Mg(s) + 2HNO₃(aq) → Mg(NO₃)₂(aq) + H₂(g).

Answer 45:
(a) Sodium > Calcium > Magnesium > Zinc > Iron > Lead > Copper
(b) When a zinc rod is dipped in a solution of copper sulphate, zinc, being a more reactive metal than copper, will displace copper from copper sulphate solution. The blue colour of the copper sulphate solution gradually fades due to the formation of the green-coloured zinc sulphate. The red-brown colour of copper will be deposited on the zinc rod.
Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)

Exercise : Solution of Questions on page Number : 134

Answer 46:
When the copper plate is dipped in AgNO₃ solution, silver from the solution gets deposited on the copper plate. This happens because copper is a more reactive metal than silver and it displaces silver from the silver nitrate solution.
2AgNO₃(aq) + Cu(s) → Cu(NO₃)₂(aq) + 2Ag(s)

Answer 47:
Five uses of metals are:
Metals are ductile and can be drawn into wires. Example: copper and aluminium
House-hold utensils and factory equipment can be made using metals because they are malleable. Example:Iron, copper and aluminium.
Iron can be protected from rusting by galvanising it with zinc.
Mercury, a liquid metal, is used in thermometers.
Car batteries are made out of the metal, lead.
Five uses of non-metals are:
Hydrogen is used to manufacture ammonia.
Hydrogen is also used in rocket fuel.
Graphite is used to make electrodes of electrolytic cells and dry cells.
Nitrogen, due to its inertness, is used to preserve food.
Sulphur is used to vulcanise rubber.

Answer 48:
Copper is used to make electrical wires.
Aluminium is used to make house-hold utensils and factory equipment.
In the preparation of ammonia gas by Haber’s process, iron acts as a catalyst.
Thin silver foils are used to decorate sweets.
Gold is used to make jewellery.
Liquid mercury is used in thermometers.

Answer 49:
(a) Hydrogen is used as fuel in rockets.
Carbon (as graphite) is used to make electrodes of electrolytic cells and dry cells.
Nitrogen, due to its inertness, is used to preserve food material.
Sulphur is used as a fungicide.
(b) Liquid mercury is used in thermometers.

Answer 50:
(a) Aluminium does not react with water under ordinary conditions because of the presence of a thin but tough layer of aluminium oxide on its surface, This layer of aluminium oxide prevents it from reacting with water.
(b) Sodium and magnesium are two metals which can displace hydrogen from dilute acids.
(c) Copper and silver are two metals which cannot displace hydrogen from dilute acids.

Answer 51:
(a) Sodium is kept immersed in kerosene oil because sodium is a very reactive metal that reacts vigorously with the oxygen in the air and with water. If sodium reacts with oxygen or water, it catches fire in an exothermic reaction.
(b) White phosphorus is kept immersed in water because it starts burning spontaneously when it comes into contact with air. But it does not react with water.
(c) No, we cannot keep sodium immersed in water because it reacts vigorously even with cold water to form sodium hydroxide, hydrogen gas and a huge amount of heat.
2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g) + HEAT

Answer 52:
(a) Potassium reacts violently with water to form potassium hydroxide and hydrogen gas. The huge amount of heat evolved in the reaction will immediately burn the hydrogen gas produced in the reaction.
2K(s) + 2H₂O → 2KOH(aq) + H₂(g) + HEAT
(b) Red hot iron reacts with steam to form iron (II, III) oxide and hydrogen.
3Fe(s) + 4H₂O → Fe₃O₄(s) + 4H₂(g)
(c) When dilute hydrochloric acid is added to a reactive metal, hydrogen gas is produced.

Answer 53:
(a) Sodium displaces hydrogen from dilute hydrochloric acid.
2Na(s) + 2HCl(aq) → 2NaCl(aq) + H₂(g)
(b) Magnesium and aluminium are two metals that can displace hydrogen from dilute hydrochloric acid.

Answer 54:
(a) Sodium reacts with water vigorously to form sodium hydroxide and hydrogen gas with a large amount of heat.
2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g) + HEAT
(b) Magnesium does not react with cold water.
(i) However, it reacts with steam rapidly to form magnesium hydroxide and hydrogen gas.
Mg(s) + H₂O(g) → Mg(OH)₂(aq) + H₂(g)
(ii) Magnesium reacts very rapidly with steam to form magnesium oxide and hydrogen gas.
Mg(s) + H₂O(g) → MgO(s) + H₂(g)
(c) Aluminium does not react with cold water. But it reacts with steam to form aluminium oxide and hydrogen gas.
2Al(s) + 3H₂O(g) → Al₂O₃(s) + 3H₂(g)

Answer 55:
Sodium, magnesium and copper can be arranged based on their reactivity with water. Sodium reacts violently with cold water because it is the most reactive of the three. Magnesium does not react with hot or cold water; it reacts with only steam. Copper does not react even with steam and it is the least reactive of the three.
These three metals can be arranged based on their reactivity with a dilute acid as well. Sodium reacts with dilute hydrochloric acid violently. Magnesium reacts with dilute hydrochloric acid but less rapidly than sodium. Copper is the least reactive and it does not react with dilute hydrochloric acid.
So the order of their decreasing reactivity is sodium > magnesium > copper.

Answer 56:
(a) When aluminium oxide reacts with hydrochloric acid, it behaves as a basic oxide:
Al₂O₃(s) + 6HCl(aq) → 2AlCl₃(aq) + 3H₂O(l)
When aluminium oxide reacts with a base like sodium hydroxide, it behaves as an acidic oxide:
Al₂O₃(s) + 2NaOH(aq) →2NaAlO₂(aq) + H₂O(l)
(b) Aluminium oxide reacts with both acids and bases and so it is called an amphoteric oxide.
(c) Zinc oxide is another metal oxide that behaves like aluminium oxide.

Answer 57:
(a) When calcium reacts with water, it forms calcium hydroxide and hydrogen gas. Due to the formation of hydrogen bubbles that stick to the surface of calcium, it starts floating on water.
Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g)
(b) The chemical equation of the reaction between iron and dilute sulphuric acid is as follows:
Fe(s) + H₂SO₄(aq) → FeSO₄(aq) + H₂(g)
When the hydrogen gas produced is ignited with a burning matchstick, the gas burns with a ‘pop’ sound and a small explosion takes place.

Answer 58:
Take a torch bulb fitted with a holder and connect it to a dry cell using connecting wires, as shown in the figure below. There is a gap between the ends of the crocodile clips A and B; so, no current flows in the incomplete circuit. Hence, the bulb does not light up.

Metals are good conductors of electricity. Hence, if samples of metals are inserted between the clips A and B, the sample will allow an electric current to pass through it and the bulb will light up. But non-metals do not conduct electricity. Hence, the samples of non-metals do not allow any electric current to pass through them and the bulb will not glow.

Answer 59:
Five physical properties of metals are:
Metals are malleable and ductile.
Metals are good conductors of heat and electricity.
Metals are lustrous (shiny) and can be polished.
Metals are solids at room temperature (except mercury, which is liquid).
Metals are tough and strong.
Five physical properties of non-metals are:
Non-metals are brittle. They are neither malleable nor ductile.
Non-metals are bad conductors of heat and electricity (except graphite).
Non-metals are non lustrous (dull) and cannot be polished (except iodine).
Non-metals may be solids, liquids or gases at room temperature.
Non-metals are neither tough nor strong.

Answer 60:
(a) Metals are generally strong. But sodium is not a strong metal and it cannot support heavy objects without breaking.
Metals are generally hard. But sodium is a soft metal and can be cut even with a knife.
Non-metals are generally soft. But carbon in the form of diamond is extremely hard.
Non-metals are generally non-lustrous. But carbon in the form of diamond is a lustrous (shiny) substance.
(b) Sodium and cesium are the two metals whose melting points are so low that they melt when held in hand.

Answer 61:
Metals, when exposed to air for a long time, become dull due to the formation of a thin layer of oxides, carbonates or sulphides on their surfaces. This is because they react with various gases present in the atmosphere. This is why metals corrode. But their brightness can be restored by rubbing them with a sand paper. Then the outer corroded layer of the metals is removed and they become shiny again.

Answer 62:
(a) Metals are generally solid materials that conduct heat and electricity. They are malleable and ductile and also lustrous, hard, strong, heavy and sonorous. Iron, aluminium, copper, gold and silver are five metals.
(b) Sodium is a metal that is so soft that it can be cut with a knife.
(c) Silver is the metal which is the best conductor of heat and electricity.
(d) When a metal reacts with dilute hydrochloric acid, it forms a metal chloride salt and hydrogen gas.
For example, sodium reacts with dilute hydrochloric acid to form sodium chloride salt and hydrogen gas.
2Na(s) + 2HCl(aq) →2NaCl(aq) + H₂(g)
(e) (i) Magnesium reacts with dilute hydrochloric acid to form magnesium chloride and hydrogen gas.
Mg(s) + 2HCl(aq) →MgCl₂(aq) + H₂(g)
(ii) Aluminium reacts with dilute hydrochloric acid to form aluminium chloride and hydrogen gas.
2Al(s) + 6HCl(aq) → 2AlCl₃(aq) + 3H2(g)
(iii) Zinc reacts with dilute hydrochloric acid to form zinc chloride and hydrogen gas.
Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H2(g)
(iv) Iron reacts with dilute hydrochloric acid to form iron (II) chloride and hydrogen gas.
Fe(s) + 2HCl(aq) → FeCl₂(aq) + H₂(g)

Answer 63:
(a) Non-metals are elements that do not show metallic characteristics, such as conductivity of electricity and heat, malleability and ductility.They are non-lustrous, generally soft and non-sonorous. Hydrogen, nitrogen, oxygen, carbon and silicon are five examples of non-metals.
(b) Carbon in the form of graphite is a non-metal that conducts electricity.
(c) Iodine is a non-metal that is lustrous (shining surface).
(d) Carbon in the form of diamond is a non-metal, which is extremely hard.
(e) Non-metals react with oxygen to form acidic or neutral oxides. The oxide is covalent in nature as it is formed by the sharing of electrons.When carbon burns in air (oxygen), it forms an acidic oxide called carbon dioxide.
For example, the non-metal, carbon reacts with oxygen:
C(s) + O₂(g) →CO₂(g)
The product formed is acidic in nature. It can be demonstrated by dissolving carbon dioxide in water to form carbonic acid. This resultant solution or carbonic acid, when added to blue litmus solution, changes the solution’s colour to red. This shows that the oxide formed is acidic in nature.

Answer 64:
(a) The arrangement of metals in a vertical column in the order of their decreasing reactivity is called the reactivity series of metals.
The increasing order of these metals according to their reactivity with water is:
Iron < Zinc < Magnesium < Sodium
(b) Hydrogen is not a metal but it has been assigned a place in the reactivity series of metals because like metals, it also loses electrons and forms positive ions, H+.
(c) Lead is the metal that is more reactive than hydrogen and copper is the metal that is less reactive than hydrogen.
(d) Zinc is the metal that can displace copper from copper sulphate solution and silver is the metal that does not displace copper from copper sulphate solution.
(e) Copper is the metal that can displace silver from silver nitrate solution and gold is the metal that cannot displace silver from silver nitrate solution.

Answer 65:
(a)

(b)

(c) (i) Sodium reacts violently with water to form sodium hydroxide and hydrogen gas, which is the property of a metal.
(ii) Sodium reacts with dilute acids and displaces hydrogen gas from the acids and forms sodium salt, which is the property of a metal.
(iii) Sodium exists in solid state at room temperature, which is the property of a metal.
(d) (i) Sulphur is not lustrous, which shows that it is a non-metal.
(ii) Sulphur is a non-sonorous material, which shows that it is a non-metal.
(iii) Sulphur reacts with oxygen to form sulphur dioxide that is acidic in nature. This shows that it is a non-metal.
(e) Hydrogen is the non-metal that has been placed in the reactivity series of metals because it loses electrons to form positive ions (H⁺) like metals.

Answer 66:
(a) Na and K
Because Na and K are metals whose oxides are basic in nature, which can turn phenolphthalein solution pink.

Answer 67:
(a) a metal
Because malleability and ductility are the properties of metals.

Answer 68:
(d) Na₂O
Because Na₂O is a metal oxide that is basic in nature.

Answer 69:
(a) K
Because K is a metal, its oxide K₂O is a basic oxide.

Answer 70:
(b) C
Because C is a non-metal, its oxide CO₂ is an acidic oxide.

Answer 71:
(c) Gold
Because gold is less reactive than silver. The other metals are more reactive than silver and can displace it from silver nitrate solution.

Answer 72:
(d) calcium
Calcium lies above the other three metals in reactivity series.

Answer 73:
(b) silver
Because silver lies below other metals in the reactivity series.

Answer 74:
(b) sulphur
Because sulphur reacts with hydrogen to form a covalent hydride, H₂S that has the smell of rotten eggs.

Answer 75:
(b) Al₂O₃
Al₂O₃ can react with acids as well as bases to form salt and water.

Answer 76:
(d) aluminium and zinc
Both aluminium and zinc oxides react with acids and bases to form salt and water.

Answer 77:
(b) carbon
Carbon forms two oxides, CO and CO₂. The oxide CO is neutral and CO₂ is acidic in nature.

Answer 78:
(c) potassium and magnesium
Potassium and magnesium are metals whose oxides are basic in nature. These oxides turn red litmus solution to blue.

Exercise : Solution of Questions on page Number : 136

Answer 79:
(d) phosphorus and sulphur
Phosphorus and sulphur are non-metals whose oxides are acidic in nature. These oxides turn blue litmus solution to red.

Answer 80:
(c) an amphoteric oxide
Zinc oxide can react with both acids and bases to form salt and water.

Answer 81:
(c) copper and tin
Copper lies below hydrogen and tin lies above hydrogen in the reactivity series of metals.

Answer 83:
(a) calcium
Calcium reacts with oxygen to form calcium oxide with a high melting point. This compound is also soluble in water.

Answer 84:
(b) Ag
Ag will be replaced from the solution of its salt by the other three metals.

Answer 85:
(d) Na
Na is soft and can be cut with a knife. It is very reactive and cannot be kept in open air. It reacts vigorously with water.

Answer 86:
(d) Hg
Mercury (Hg) is the metal that exists in liquid state at room temperature.

Answer 87:
(c) bromine
Bromine is the non-metal that is a liquid.

Answer 88:
(d) CuSO₄ + Fe
Iron (Fe) is a more reactive metal than copper, which can displace copper from copper sulphate.

Answer 89:
(a) The oxide E₂O is basic in nature because it turns red litmus paper blue.
(b) The element E is a metal because metal oxides are basic in nature.
(c) Sodium (Na) is an element like E. It forms the oxide Na₂O on reacting with oxygen, which turns red litmus paper blue.

Answer 90:
(a) The oxide A₂O₃ is amphoteric, which can react with both acids and bases to form salt and water.
(b) The oxide BO is amphoteric, which can react with both acids and bases to form salt and water.
(c) Aluminium is a metal like A, which forms Al₂O₃ on reacting with oxygen.
(d) Zinc is a metal like B which forms ZnO on strongly heating in air (oxygen).

Answer 91:
(a) The oxide XO is neutral in nature as it has no action on litmus solution.
(b) The oxide XO₂ is acidic in nature as it turns litmus solution red.
(c) The element X is a non-metal because it forms an acidic and neutral oxide, which is the property of a non-metal.
(d) Carbon is a non-metal like the element X.

Answer 92:
(a) Gold, being less reactive than copper, cannot displace copper from copper sulphate solution and hence, no reaction occurs.
(b) Copper reacts with copper sulphate to form copper and copper sulphate solution. So, practically no reaction occurs between them.
(c) Zinc is more reactive than copper and hence, displaces copper from its solution to form zinc sulphate solution and copper metal.
Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)
(d) Mercury, being less reactive than copper, cannot displace copper from copper sulphate solution and hence, no reaction occurs.

Answer 93:
(a) Sodium chloride is a metal chloride and its formula is NaCl.
Hydrogen chloride is a non-metal chloride and its formula is HCl.
(b) Metal chlorides are ionic chlorides, which are electrolytes that can conduct electricity. However, non-metal chlorides are covalent chlorides, which are non-electrolytes that do not conduct electricity.
(c) They differ in this property because of the bonding in the chlorides. Metal chlorides have ionic bonds but non-metal chlorides have covalent bonds.

Answer 94:
The metal M is more reactive than lead because M displaces lead from lead acetate solution, which can be done only by an element that is more reactive lead.

Exercise : Solution of Questions on page Number : 137

Answer 95:
In the first reaction, Fe displaces Cu from CuSO₄ solution. So Fe is more reactive than Cu.
In the second reaction, Zn displaces Fe from FeSO₄ solution. So Zn is more reactive than Fe.
Hence it can be concluded that Zn is the most reactive metal and Cu is the least reactive metal out of zinc, copper and iron.

Answer 96:
Reactions (a) and (c) will not occur because copper is less reactive than magnesium. So, it cannot displace magnesium from its salt solution, the equation of which is shown in reaction (a).
Similarly, iron is less reactive than magnesium. So, it cannot displace magnesium from its salt solution, the equation of which is shown in reaction (c).

Answer 97:
The metal B will be nearer to the top of the activity series of metals because this metal is so reactive that it reacts with most elements to form its compounds. But metal A is less reactive as it exists in free state without reacting with other elements.

Answer 98:
The metal K is most likely to occur in a free state in nature because it is the least reactive among other metals. Since it is the least reactive, it will not react with other elements.

Answer 99:
(a) (i) Aluminium does not react with cold or hot water but it reacts with steam.
(ii) Gold does not react with any physical state of water.
(b) Sodium is more reactive than calcium. The reaction between sodium and water produces a large amount of heat, which causes the evolved hydrogen to burn and catch fire. But in the reaction between calcium and water, no heat is produced and hence the evolved hydrogen does not catch fire.

Answer 100:
Zinc is more reactive than copper and hence zinc displaces copper from copper sulphate solution to form zinc sulphate solution, which is of green colour, and copper. It is due to formation of the green zinc sulphate solution that the blue colour of copper sulphate gets lighter and lighter.
Zinc from the rod reacts with the solution to form zinc sulphate solution. So the plate has a number of small holes in it.
Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)

Exercise : Solution of Questions on page Number : 167

Answer 1:
(a) Covalent bond is formed by the sharing of electrons between two atoms.
(b) Ionic bond is formed by the transfer of electrons from one atom to another.

Answer 2:
Carbon dioxide is a carbon containing molecule which has two double bonds. It is represented as O=C=O.

Answer 3:
The electron dot structure of CO₂ can be represented as:
O…. :: C : O…. :

Answer 4:
(a) Potassium is a metal and bromine is a non-metal. Hence the type of bond formed between potassium and bromine is ionic bond.
(b) Carbon and bromine are both non-metals. Hence the type of bond formed between them is covalent bond.

Answer 5:
(a) The particles that have more or less electrons than normal atoms are called ions.
(b) The particles that have more electrons than normal atoms are called anions.
(c) The particles that have less electrons than normal atoms are called cations.

Answer 6:
(a) Na+ contains one less electron than the Na atom (11 electrons). So it contains 11 − 1 = 10 electrons.
(b) Cl⁻ contains one more electron than the Cl atom (17 electrons). So it contains 17 + 1 = 18 electrons.

Answer 7:
Element X is oxygen (atomic number 8). Oxygen needs two more electrons to complete its noble gas configuration. The element Y is magnesium (atomic number 12). Magnesium has two extra electrons than are needed to achieve a stable configuration. Hence, magnesium donates two electrons to the oxygen atom to attain a stable configuration.
So, Mg becomes Mg²⁺ and O becomes O2^– as ions.

Answer 8:
(a) (i) The electronic configuration of a magnesium atom (atomic no. 12) is: K L M
2 8 2
(ii) The electronic configuration of a magnesium ion (atomic no. 10) is: K L
2 8
(b) (i) The electronic configuration of a sulphur atom (atomic no. 16) is: K L M
2 8 6
(ii) The electronic configuration of a sulphide ion (atomic no. 18) is: K L M
2 8 8

Answer 9:
In a solid compound that has a high melting point, that does not conduct electricity in the solid state but becomes a good conductor in the molten state, the chemical bonds between atoms will be ionic.

Answer 10:
False. The aqueous solution of an ionic compound conducts electricity because there are plenty of free ions in the solution. (But not the free electrons.)

Answer 11:
The chemical bond present in hydrogen chloride is a covalent bond. In hydrogen chloride, one electron each from hydrogen and chlorine are shared between the two atoms.
The chemical bond present in an oxygen molecule is covalent bond. In an oxygen molecule, each oxygen atom shares one electron to complete its outermost shell.

Answer 12:
(i) The electron-dot structure of NaCl:

(ii) The electron-dot structure of Cl₂:

Answer 13:
The chemical bond present in a water molecule is covalent bond because one oxygen atom shares its two electrons with two hydrogen atoms.
The electron-dot structure of a water molecule is represented as:

Answer 14:
The chemical bond present in methane (CH₄) is covalent bond as a carbon atom shares its four valence electrons with four hydrogen atoms to form one methane molecule.
The chemical bond present in sodium chloride (NaCl) is ionic bond as a sodium atom transfers one electron to a chlorine atom to form the ionic bond in NaCl.

Answer 15:
Covalent compounds have usually low melting points and boiling points. But ionic compounds have high melting points and boiling points.
An example for a covalent compound is methane (CH₄).
An example for an ionic compound is sodium chloride (NaCl).

Answer 16:
(i) Covalent bond is the chemical bond present in an H₂ molecule as one hydrogen atom shares its electrons with another hydrogen atom.
The electron-dot structure is:

(ii) Covalent bond is the chemical bond present in CH₄ as a carbon atom shares its electrons with four hydrogen atoms.
The electron-dot structure is:

(iii) Covalent bond is the chemical bond present in a Cl₂ molecule as one chlorine atom shares its electrons with another chlorine atom.
The electron-dot structure is:

(iv) Covalent bond is the bond present in O2 as one oxygen atom shares its electrons with another oxygen atom.
The electron-dot structure is:

Answer 17:
Argon is the inert gas that resembles the Cl atoms in electronic configuration in a Cl₂ molecule. This electronic configuration is  K L M.
2  8   8

Answer 18:
The ionic compounds are sodium chloride, ammonium chloride and magnesium chloride. The covalent compounds are urea, cane sugar, hydrogen chloride, carbon tetrachloride, ammonia and alcohol.

Answer 19:
(i)  A molecule containing a single covalent bond: hydrogen molecule (H − H)
(ii) A molecule containing a double covalent bond: oxygen molecule (O=O)
(iii) A molecule containing a triple covalent bond: nitrogen molecule (N≡N)
(iv) A compound containing an ionic bond: sodium chloride (NaCl)

Exercise : Solution of Questions on page Number : 168

Answer 20:
(i) Two atoms of the same element combine to form a molecule. The bond between them is known as a covalent bond.
(ii) Two chlorine atoms combine to form a molecule. The bond between them is known as a covalent bond.
(iii) In forming an oxygen molecule, two electrons are shared by each atom of oxygen.
(iv) In forming an N₂ molecule, three electrons are shared by each atom of nitrogen.
(v) The number of single covalent bonds in a C₂H₂ molecule is two.
(vi) Melting points and boiling points of ionic compounds are generally higher than those of covalent compounds.

Answer 21:
(a) The chemical bond that is formed between two atoms by the sharing of electrons is known as a covalent bond.
(i) A covalent bond exists in CCl₄.
(ii) An ionic bond exists in CaCl₂.
(b) The chemical bond that is formed by the transfer of electrons between two atoms is known as an ionic bond.
Covalent bond is the chemical bond present in an oxygen molecule.

Answer 22:
(a) An electrically-charged atom (or group of atoms) is called an ion. it is formed by the loss or gain of an electron by an atom.
Ions are of two types: cations and anions.
For example: A sodium ion (Na+) is formed when a sodium atom loses one electron. A sodium ion is a cation.
A chloride ion (Cl^–) is formed when a chlorine atom gains one electron. A chloride ion is an anion.
(b) (i) The charge on a cation is positive.
(ii) The charge on an anion is negative.
(c) The cation present in MgCl₂ is a magnesium ion that is represented as Mg²⁺ and the anion present is a chloride ion that is represented by Cl^-.

Answer 23:
(a) In a chlorine molecule, the atoms bonded by a covalent bond as a chlorine atom needs one electron to complete its octet and shares one electron with another chlorine atom.
(b) The atomic number of chlorine is 17 and its electronic configuration is 2, 8, 7. It needs one more electron to complete its octet. Chlorine gets this electron by sharing with another atom. So each chlorine atom shares one electron to form a chlorine molecule.

Answer 24:
(a) (i) Ionic compounds are compounds that are formed by the transfer of electrons by an atom to another atom.
Example: Sodium chloride (NaCl) is an ionic compound, where sodium transfers one electron to chlorine atom.
(ii) Covalent compounds are compounds that are formed by the sharing of electrons between two or more atoms.
Example: Hydrogen (H₂) is a covalent compound, where each hydrogen atom shares one electron to form a stable compound.

(b)

Answer 25:
(a) Covalent compounds are made up of electrically neutral molecules. So the force of attraction between the molecules is very weak. Only a small amount of heat energy is required to break these weak molecular forces, due to which covalent compounds have a low melting point.
(b) Ionic compounds have generally high melting points because ionic compounds are composed of positively and negatively charged ions. So there is a strong force of attraction between these ions. A large amount of heat energy is required to break this strong force of attraction and hence they have a high melting point.

Answer 26:
(a)

(b) Sodium chloride and sugar can be distinguished by the electrical conductivity test. Sugar, being a covalent compound, does not conduct electricity when dissolved in water but sodium chloride when dissolved in water conducts electricity.

Answer 27:
(a) An ionic compound consists of ions held by strong forces in solid state. But when an ionic compound dissolves in water to form a solution, the constituent ions get separated and they disperse across the solution. This helps in conducting an electric current through the solution. Covalent compounds are formed by the sharing of electrons. So ions that conduct electricity are not involved in these compounds. Hence covalent compounds do not conduct electricity.
(b) The compounds that conduct electricity are MgCl₂, NaCl and Na₂S. These compounds are ionic in nature So conduct electricity. The compounds that do not conduct electricity are CS₂ and CCl₄. These compounds are covalent in nature. Hence they do not conduct electricity.

Answer 28:
(a) An ionic compound that contains chlorine is sodium chloride (NaCl) and a covalent compound that contains chlorine is hydrogen chloride (HCl).
(b) The test to find out which water soluble compound, A or B, is ionic can be done by the electrical conductivity test. The compound solution that conducts electricity must be ionic in nature and the other compound solution that does not conduct electricity must be covalent in nature.

Answer 29:
A solution of cane sugar does not conduct electricity because cane sugar is a covalent compound, which is bonded by the sharing of electrons. In the solution, it does not have ions to conduct electrical charges across the solution. But common salt consists of sodium and chloride ions and is formed by the transfer of one electron of sodium to a chlorine atom. When this salt dissolves in water to form its solution, ions get dispersed across the solution due to which the solution conducts electricity across the solution.

Answer 30:
(a) Mg₃N₂
(b) Li₂O
(c) AlCl₃
(d) KH

Answer 31:
(a) The elements in group 18 of the periodic table, which do not combine with other elements are known as noble gases. These elements are helium, neon, argon, krypton, xenon and radon. The important characteristic of the electronic configuration of the noble gases is that they have completely filled outermost shells or valence shells, which is the reason for the inertness of these elements.
(b) The atoms of elements undergo chemical bonding (or chemical combination) to attain the noble gas electronic configuration and become more stable. By chemical bonding, atoms share or transfer their electrons to make their outermost shells completely filled and thus attain stability.

Answer 32:
(i) The electron-dot structure of magnesium and oxygen is:

(ii)
(iii) In this compound, a magnesium ion (Mg²⁺) and an oxide ion (O^2-) are present as a cation and an anion, respectively.

Answer 33:
The electron-dot structure of a hydrogen chloride molecule is:

It is formed by sharing one electron by the hydrogen and chlorine atoms.
(i) The H atom in HCl resembles helium gas in its electron arrangement by sharing one electron with the chlorine atom to get two electrons in its outermost shell.
(ii) The Cl atom in HCl resembles argon gas in its electron arrangement by sharing one electron with the hydrogen atom to get eight electrons in its outermost shell. Its electronic configuration becomes 2, 8, 8.

Answer 34:
(i) Calcium and oxygen react to form calcium oxide (CaO) by ionic bonding. Calcium contains two electrons in its outermost shell and oxygen contains six electrons in its outermost shell. So the calcium atom transfers two electrons to the oxygen atom to attain the noble gas configuration for both atoms.
(ii) Carbon and chlorine react to form carbon tetrachloride (CCl₄) by covalent bonding. Carbon contains four electrons in its outermost shell and chlorine contains seven electron in its outermost shell. So carbon shares electrons electrons with four chlorine atoms (one electron from each chlorine atom) to attain stability.
(iii) Hydrogen and chlorine react to form (HCl) by covalent bonding. Hydrogen contains one electron in its outermost shell and chlorine also contains one electron in its outermost shell. So the hydrogen and chlorine atoms share one electron from each atom to attain stability.

Exercise : Solution of Questions on page Number : 169

Answer 35:
The electronic configuration of sodium is 2, 8, 1. The outermost shell contains one electron. For the atom to be stable, it should lose one electron and thus attain the noble gas configuration of 2, 8.
Na ^– e^– → Na⁺
The electronic configuration of the chlorine atom is 2, 8, 7. The outermost shell contains seven electrons. For the atom to be stable, it requires one electron and thus attain the noble gas configuration of 2, 8, 8.
Cl ⁺ e^– → Cl^–
Hence sodium donates one electron to the chlorine atom when they react with each other to form a stable compound, sodium chloride, NaCl. This type of bonding that takes place through transfer of electrons is known as ionic bonding.

Answer 36:

Cations are formed when an atom donates its electrons to another atom to attain the noble gas configuration and become stable.
Anions are formed when an atom gains electrons from another atom to complete its outermost shell or attain the noble gas configuration and become stable.
An example of a cation is a sodium ion (Na+) that is formed by losing one electron.
An example of an anion is a chloride ion (Cl-) that is formed by gaining one electron.

Answer 37:
The atomic number of nitrogen is 7. Its electronic configuration is 2, 5. Hence, it contains five electrons in its outermost shell.Three electrons from each nitrogen atom are shared to complete its octet. This sharing of electrons results in covalent bonding in a nitrogen molecule.

Answer 38:
(i) The electron-dot structure of CO₂ is:

Both oxygen and carbon share their two electrons to form a covalent bond in carbon dioxide, CO₂.
(ii) The electron-dot structure of MgO is:
Mg²⁺: O:….2-
Magnesium donate its two electrons to the oxygen atom to form an ionic bond in magnesium oxide, MgO .
(iii) The electron-dot structure of H₂O is:

The oxygen atom shares its one electron with each hydrogen atom to form a covalent bond in the water molecule.
(iv) The electron-dot structure of HCl is:
H:Cl….:
The hydrogen atom shares its one electron with a chlorine atom to form a covalent bond.
(v) The electron-dot structure of MgCl₂ is:

The magnesium atom transfers its one electron to each chlorine atom to form an ionic bond.

Answer 39:
The atomic number of oxygen is 8. Its electronic configuration is 2, 6. Hence it has six electrons in its outermost shell.

In an oxygen molecule, one oxygen atom shares its two electrons with another oxygen atom. Hence this type of bonding is called covalent bonding.

Answer 40:
(i) The electron-dot structure of KCl is:

In KCl, the potassium atom transfers its 1 electron to the chlorine atom to form an ionic bond.
(ii) The electron-dot structure of NH₃ is:

In NH3, each hydrogen atom shares its one electron with the nitrogen atom to form a covalent bond.
(iii) The electron-dot structure of CaO is:

In CaO, the calcium atom transfers its two electrons to the oxygen atom to form an ionic bond.
(iv) Electron-dot structure of N₂ is

In N₂, one nitrogen atom shares its three electrons with another nitrogen atom to form a covalent bond.
(v) The electron-dot structure of CaCl₂ is:

In CaCl₂, one calcium atom transfers its two electrons to the two chlorine atoms to form an ionic bond.

Answer 41:
The ions of salt in solid state are bonded with strong inter-particle forces. Hence, they are not free to move in solid state and cannot conduct electricity. However, when this salt melts, its constituent ions get separated from each other. Thus, they are free to move across the melted salt and conduct electricity.

Answer 42:
(a) (i) Atomic number of sodium is 11.
Its electric configuration is K L M 2 8 1.
(ii) Atomic number of chlorine is 17.
Its electronic configuration is K L M2 8 7.
(b) (i) In a sodium atom, the number of electrons present in its outermost shell (M shell) is one.
(ii) In a chlorine atom, the number of electrons present in its outermost shell (M shell) is seven.
(c) Sodium and chlorine contain one and seven electrons, respectively, in their outermost shells. Hence, sodium transfers its one electron to chlorine atom and their octets get stabilised.
Na. + :Cl:…→ Na+:Cl….:- or NaCl
In a sodium chloride molecule, sodium atom transfers its one electron to chlorine atom to form an ionic bond.
(d) Sodium chloride contains positively charged sodium atom and negatively charged chlorine atom. Due to these oppositely charged species, there is a strong intermolecular force between them. Hence, it requires huge amount of energy to break this strong intermolecular force and melt the salt. Therefore, sodium chloride has a high melting point.
(e) In the electrolytic refining of impure copper metal, anode is the electrode at which oxidation takes place and cathode is the electrode at which reduction takes place.
Hence, at anode, a thick block of impure copper metal is used from which pure metal oxidises to copper ion in the solution.
At cathode, a thin strip of pure copper metal is used where copper ions from the solution reduce to copper metal and get deposited on the strip.

Answer 43:
(a) (i) Magnesium atom contains 12 electrons.
Its electron arrangement can be written as 2 K8 L2 M.
(ii) Oxygen atom contains eight electrons.
Its electron arrangement can be written as 2 K6 L.
(b) (i) The valence shell of a magnesium atom contains two electrons.
(ii) The valence shell of an oxygen atom contains six electrons.
(c)
In a magnesium oxide molecule, magnesium atom transfers its two electrons to oxygen atom to form ionic bond.
(d) The solvent in which ionic compounds are generally soluble is water.
(e) Aqueous solution of ionic compounds is able to conduct electricity because in aqueous solution, the strong force of attraction between ions is vanished. Their constituent ions get separated and become free to move across the solution. Due to this movement of ions, aqueous solution of ionic compounds conducts electricity.

Answer 44:
(a)
i) Sodium atom contains 11 electrons.
Its electronic configuration can be written as 2K 8L 1M .
(ii) Oxygen atom contains eight electrons.
Its electron arrangement can be written as 2K 6L .
(b) (i) Sodium atom contains one electron in its outermost shell.
(ii) Oxygen atom contains six electrons in its outermost shell.
(c) In sodium oxide molecule, two sodium atoms transfer their one electron to one oxygen atom to form ionic bonds.

(d) Ionic compounds are generally hard because they consist of oppositely-charged ions. These ions are strongly attracted to each other and form a hard crystalline solid.
(e) The ionic compounds in solid state are bonded with strong intermolecular forces and are not free to move. Therefore, they cannot conduct electricity. However, when this salt melts, its constituent ions are separated from each other and become free to move across the melted salt that can conduct electricity.

Answer 45:
(a) (i) Magnesium atom contains 12 electrons.
Its electron arrangement can be written as 2K 8L 2M.
(ii) Chlorine atom contains 17 electrons.
Its electron arrangement can be written as 2K 8L 7M .
(b) (i) Magnesium atom in its valence shell contains two electrons.
(ii) Chlorine atom in its valence shell contains seven electrons.
(c) In magnesium chloride molecule, magnesium atom transfers its two electrons to two chlorine atoms to form ionic bonds.

(d) Magnesium chloride will conduct electricity because it is an ionic compound. On melting or dissolving in water, it conducts electricity due to the separation of charged ions, which move freely across the solution.
(e) Covalent compounds are generally poor conductors of electricity because they do not contain ions that can move freely and pass electricity.

Answer 46:
(a) 18
Because X⁺ ion contains one less electron than X.

Answer 47:
(b) 18
Anion Y- has one more electron than its neutral atom. Y atom has 17 electrons and therefore, in Y-, number of electrons will be 18 (17 + 1).

Answer 48:
(d) B and D
Element B has the electronic configuration of 2,6. It requires 2 electrons to complete its octet. On the other hand, element D has the electronic configuration of 2,8,2. It requires to release 2 electrons to complete its octet. Thus, both atoms react to form ionic bonds by transfer of electrons.

Answer 49:
(c) P and S
Element P needs 4 electrons to complete its octet. They can be shared with element S, which needs only 1 electron to complete its octet.

Exercise : Solution of Questions on page Number : 170

Answer 50:
(b) CCl₄
Because it is a covalent compound.

Answer 51:
(d) Y is a non-metal and Z is a metal.
Element Y has 1 less electron to complete its octet which is a property of non-metals. On the other hand, element ​Z has 2 extra electrons to become stabilised which is a property of metals.

Answer 52:
(b) electrical conductivity in solid state
Because ionic compounds conduct electricity only in molten state or when dissolved in water to form aqueous solution.

Answer 53:
(c) 8 or 2
Helium is the only noble gas that has 2 electrons in its valence shell. Other noble gases have 8 electrons in their valence shells.

Answer 54:
(c) X²⁻
Element X needs 2 electrons to complete its octet. Therefore, it forms X²⁻ anion.

Answer 55:
(d) Y³⁺
Number of protons is equal to number of electrons in an atom. Hence, electronic configuration of element Y is 2,3. Thus, it becomes stabilised by donating its 3 electrons to form Y³⁺.

Answer 56:
(b) HCl and CCl₄
Both these compounds are formed by sharing of electrons and hence, they form covalent bonds and not ionic bonds.

Answer 57:
(b) low melting point
Compound Z is an ionic compound formed by transfer of electrons. Ionic compounds have high melting points.

Answer 58:
(d) Carbon tetrachloride
It is a covalent compound.

Answer 59:
(d) lithium ion battery
Because lithium ion is a good conductor of electricity.

Answer 60:
(c) 10
Number of protons is equal to the number of electrons in an atom. It is given that one atom of an element X contains 8 electrons.
Therefore, number of electrons in its ion X²⁻ = 10 + 2 = 12

Answer 61:
(c) 18
Number of protons is equal to the number of electrons in an atom. It is given that an atom of an element Y contains 20 electrons. Therefore, number of electrons in its ion Y²+ is 18 (20 – 2).

Answer 62:
(c) He
Atomic number of helium is 2. It contains 2 electrons in its atom.

Answer 63:
(b) Oxygen
In an oxygen molecule, each oxygen atom shares its 2 electrons to complete its octet and forms double covalent bond between them.

Answer 64:
(d) nitrogen and ethyne
In a nitrogen molecule, each nitrogen atom shares its 3 electrons to form a triple bond among them. In an ethyne molecule, each carbon atom shares 3 electrons to form a triple bond among them.

Answer 65:
(c) C₂H₄
An ethene molecule (C₂H₄) contains one double bond between two carbon atoms and four single bonds between carbon and hydrogen atoms.

Answer 66:
(c) ethyne
An ethyne molecule ( H-C ≡ C-H ) contains a triple bond between two carbon atoms and two single bonds between carbon and hydrogen atoms.

Exercise : Solution of Questions on page Number : 171

Answer 67:
(a) Covalent bond is present compound X because it is formed by sharing of electrons.
(b) Compound X has a low melting point because it is a covalent compound.
(c) Being a covalent compound, it will not be a good conductor of electricity.
(d) Covalent compounds dissolve in an organic solvent. Since X is a covalent compound, it will dissolve in an organic solvent.

Answer 68:
(i) Compound Y has ionic bonds because it is formed by transfer of electrons.
(ii) Its melting and boiling points will be high because of the strong intermolecular forces between them.
(iii) It will be a good conductor of electricity because of the presence of ions in it.
(iv) It will not be dissolved in an organic solvent because of its ionic nature.

Answer 69:
(a) Elements Y and Z combine to form an ionic compound by transfer of one electron from Z to Y.
(b) Elements X and Y will react to form a covalent compound because atom X can react with 4 atoms of Y to share their one electron.

Answer 70:
The compound formed by elements A and B has covalent bonds between their atoms. One atom of element A reacts with four atoms of element B to share its one electron.
Its electron-dot structure is represented as:

Answer 71:
Compound XY₂ has ionic bonds in nature because it is formed by transfer of electrons.
Two properties of compound XY₂ are:
It has high melting and boiling points.
It conducts electricity in molten state or when dissolved in water (but not in solid state).

Answer 72:
Compound AB₂ is ionic in nature.
Explanation: Atom A has two electrons in its outermost shell and atom B needs one electron to complete its octet. Atom A transfers its two electrons to two atoms of B (one electron to each atom B) and gets stabilised by forming ionic bonds.
When dissolved in water, the ions of this ionic compound get separated from each other and conduct electricity across the solution.

Answer 73:
(a) Two atoms of A can form covalent bond between them by sharing two electrons from each atom. This allows them to complete their octets and get stabilised. The molecule so formed is A=A.
(b) Atoms A and B may react to form ionic bond by transfer of two electrons from two atoms of B to form an ionic compound AB_2.

Answer 74:
(a) When element C combines with element D, an ionic bond is formed between them by transfer of one electron from element C atom to element D atom.
(b) Element B is an inert gas because it has 8 electrons in its valence shell; i.e, it contains completely filled valence shell.
(c) Formula of the compound will be AC₂. Because element A needs two electrons to complete its octet, two atoms of element C donate two electrons to element A and get stabilised.

Answer 75:
Compound XY₂ will have ionic bonds because it is formed by transfer of electrons from atoms of element X to atoms of element ​Y.
On forming the compound XY₂, each atom of element X that has 12 electrons with an electronic configuration of 2,8,2, donates its two electrons to give X²⁺ ion that has an electronic configuration of 2,8. Similarly, each atom of Y that has 17 electrons with electronic configuration 2,8,7 completes its octet by gaining one electron to form Y- ion that has an electronic configuration of 2,8,8.

Answer 76:
(a) Element A is a metal because it can donate its one electron to attain noble gas configuration.
(b) Elements B and C are non-metals because B and C can complete their octets either by accepting or sharing the electrons.
(c) Elements A and B will combine to form an ionic bond because element A will transfer its electron to element B to attain noble gas configuration.
(d) Elements B and C will combine to form a covalent bond by sharing four electrons of one atom of element C with four atoms of element B.
(e) Element B will form an anion of valency one because element B contains one less electron to complete its octet. After gaining one electron, it becomes stabilised and forms an anion B

Exercise : Solution of Questions on page Number : 172

Answer 78:
(a) An atom of X must lose its two electrons to attain the nearest inert gas electron configuration.
(b) After losing two electrons, it will have 10 electrons with electronic configuration 2,8, which represents neon gas. So, neon gas is the nearest inert gas to X.

Answer 79:
(a) An atom of Y has an electronic configuration of 2,8,6; therefore, it must gain two electrons to achieve the nearest inert gas electron configuration.
(b) Argon gas is the nearest inert gas to Y. After gaining two electrons, it will have 18 electrons with an electronic configuration of 2,8,8, which represents argon gas.

Answer 80:
These substances are covalent in nature because bonding between covalent substances are not as strong as ionic substances. So, covalent compounds hold together with weak forces and low melting point. This is why, they vapourise easily and give their odours. However, when ionic compounds comes in contact with air, they cannot give an odour by vapourising.

Answer 81:
The formula of the chloride of element X is XCl (or X⁺Cl^–). Element X has an electronic configuration of 2,1. When it reacts with chlorine with electronic configuration 2,8,7, it transfers one electron to chlorine atom to form an ionic chloride compound.
The formula of the chloride of element Y is YCl4. Element Y has an electronic configuration of 2,4. When it reacts with chlorine with electronic configuration 2,8,7, it shares its four electrons with four chlorine atoms.
Properties of the two chlorides will be different because of the difference in the natures of bonding between them. For example, XCl, being ionic in nature, must have high melting and boiling points but YCl_4, being covalent in nature, must have low melting and boiling points.

Exercise : Solution of Questions on page Number : 191

Answer 1:
The zinc ore that gives CO₂ on treatment with a dilute acid is calamine.
Its chemical formula is ZnCO₃.

Answer 2:
Reduction is the chemical process used for obtaining a metal from its oxide by using reducing agents like carbon, sodium, aluminium or calcium.

Answer 3:
Rusting of iron can be prevented by the following two ways:
By coating the surface of iron with paint: On coating, air and moisture cannot comes in contact with iron and hence, no rusting takes place.
By applying grease or oil on the surface of iron: This method also prevents air and moisture to come in contact with iron and hence, no rusting takes place.

Answer 4:
Galvanisation is a process wherein a thin layer of zinc metal gets deposited on iron objects. This is done to prevent rusting of iron by protecting it to come in contact with air and moisture. Zinc metal, being more reactive, reacts with air to form hard layer of zinc oxide, which prevents air from passing through it.

Answer 5:
Zinc metal is used for galvanising iron because it is more reactive than iron. It reacts with air to form a hard layer of zinc oxide, which prevents air and moisture to come in contact with iron.

Answer 6:
Iron sheets are coated with zinc because zinc is a reactive metal which readily reacts with oxygen present in air to form a hard layer of zinc oxide. This layer is so hard that it prevents air and moisture from passing through it. Hence, moist air cannot come in contact with iron. This in turn prevents the rusting of iron.

Answer 7:
Iron articles are coated with paint to prevent air and moisture from coming in contact with iron and hence, to protect it from rusting.

Answer 8:
It is easier to extract metals from their oxide ores by reduction process than their carbonate and sulphide ores. Hence, carbonate and sulphide ores are usually converted into oxides during the process of extraction of metals.

Answer 9:
Aluminium powder is the reducing agent that may be used to obtain manganese from manganese dioxide.

Answer 10:
Solder is an alloy of lead and tin. It contains 50 per cent lead and 50 per cent tin.

Answer 11:
The composition of solder alloy is 50 per cent lead (Pb) and 50 per cent tin (Sn).
It has a very low melting point that is quite less than its constituting metals (Pb and Sn). Thus, solder is widely used in soldering and welding of electrical wires.

Answer 12:
Amalgam is an alloy of mercury with one or more metals. Sodium along with liquid mercury is known as sodium amalgam. Amalgam of mercury with tin, silver and zinc is widely used in dental filling.

Answer 13:
24-carat gold is pure gold. Pure gold is too soft and it is not possible to make ornaments from this soft gold. Thus, 24-carat gold is mixed with two parts of copper or silver for making jewellery. The gold used for jewellery is 22-carat gold.

Answer 14:
Electrolytic refining method is the most significant method used for refining of metals. Several metals like Cu, Zn, Au, Cr, Pb, Sn, Ni and Ag are refined by this process.

Answer 15:
Two necessary conditions required for rusting of iron are:
(i) Existence of air (oxygen)
(ii) Existence of water (or dampness)
In the absence of any of the above conditions, rusting of iron will not take place.

Answer 16:
Alloying of iron with chromium and nickel to produce stainless steel (that does not corrode) is one method where iron is not coated with anything.

Answer 17:
Two alloys of iron are steel and stainless steel. Steel consists of iron with 0.1 to 1.5 percent carbon. The elements present in stainless steel are iron, nickel and chromium.

Answer 18:
Gold, silver and platinum are least reactive metals. They do not react with air, water, acids, alkalis and other gases in the environment. Due to this, their shine lasts for years. Due to bright lustre and resistance towards corrosion, gold, silver and platinum are used to make jewellery.

Answer 19:
Silver metal becomes black in the presence of hydrogen sulphide gas in the air. Silver reacts with hydrogen sulphide gas in the air and forms a thin black layer of silver sulphide (Ag₂S) on it. Therefore, silver jewellery or ornaments become dull due to the formation of silver sulphide coating on their surface.

Answer 20:
Hydrogen sulphide gas in the air tarnishes silver articles slowly. Silver reacts with hydrogen sulphide gas in the air and forms a thin black layer of silver sulphide (Ag₂S) on it. Therefore, silver jewellery or ornaments become dull due to the formation of silver sulphide coating on their surface.

Answer 21:
Silver metal does not react with oxygen but reacts with hydrogen sulphide gas in the air and forms a thin black layer of silver sulphide (Ag₂S) on it. Therefore, silver jewellery or ornaments tarnish due to the formation of a silver sulphide coating on their surfaces.

Answer 22:
The composition of bronze is copper (90%) and tin (10%). This alloy of copper is strong and prevents corrosion.
Two uses of bronze are:
(i) It is used in the manufacturing of statues, medals etc.
(ii) It is used to make cooking vessels and propellers of ship.

Answer 23:
Aluminium is highly reactive. It reacts with moist air and forms a thin layer of aluminium oxide on it. This layer fades away the shine of aluminium. Thus, aluminium vessels lose its shine soon after use.

Answer 24:
Gold is a least reactive metal. It does not react with air, water, acids, alkalis and other gases in the environment. Due to this non-reactive nature, gold metal’s shine lasts for years and gold ornaments look new even after several years of use.

Answer 25:
Gold and platinum are highly resistant to corrosion. They are least reactive metals and therefore, they do not react with air, water, acids, alkalis and other gases in the environment.

Answer 26:
Solder is an alloy of lead and tin. Its composition is 50 percent lead (Pb) and 50 percent tin (Sn). The melting point of solder is very low and is even lower than its constituting metals (Pb and Sn). Thus, the low melting point of solder makes it suitable for welding electrical wires.

Answer 27:
Sodium and magnesium are most reactive metals (placed at the top in the reactivity series). They are very stable and cannot be reduced by carbon. They have more attraction to oxygen than carbon. Thus, carbon cannot combine with oxygen and reduce these metal oxides to metals.

Answer 28:
Sodium, potassium, calcium and magnesium are most reactive metals (placed at the top in the reactivity series). Due to their high reactivities, they are never found as free elements. They are always found in combined form.

Answer 29:
Let us name one metal in each of the following cases:
(a) Reduction with carbon: Zinc is a moderately reactive metal and thus, its oxide is reduced by carbon.
(b) Electrolytic reduction: Sodium is a highly reactive metal and it cannot be reduced by carbon or aluminium. Thus, it is reduced by electrolysis.
(c) Reduction with aluminium: Manganese is a reactive metal and it cannot be reduced by carbon. Thus, it is reduced by aluminium.
(d) Reduction with heat alone: Mercury is a least reactive metal and thus, it is reduced on heating alone.

Answer 30:
(a) The corrosion of iron is called rusting.
(b) Air (oxygen) and water are necessary for the rusting of iron.
(c) The process of depositing a thin layer of zinc on iron articles is called galvanization.
(d) Tiffin boxes are electroplated with tin but car bumpers are electroplated with chromium to protect them from rusting.
(e) The corrosion of copper produces a green coating of basic copper carbonate on its surface.
(f) Brass is an alloy of copper and zinc .
(g) Bronze is an alloy of copper and tin.
(h) The non-metal present in steel is carbon.
(i) The alloy in which one of the metals is mercury is called an amalgam
(j) The electrical conductivity and melting point of an alloy is less than that of pure metals.
(k) The rocky material found with ores is called gangue.

Exercise : Solution of Questions on page Number : 192

Answer 31:
Manganese is extracted from its oxide (Manganese dioxide or MnO₂ ) by using aluminium as the reducing agent. Because aluminium is more reactive than manganese and is placed above it in the reactivity series, aluminium can easily displace manganese from its oxide to liberate the metal.
Manganese dioxide is heated with aluminium powder to produce manganese.
3MnO₂ (s) + 4Al (s) → 3Mn (l) + 2Al₂O₃ (s) + Heat
The reaction is highly exothermic and huge amount of heat is liberated. Thus, manganese will be produced in molten (liquid) state.

Answer 32:
A thermite reaction is a reaction in which a metal oxide is reduced by using aluminium as the reducing agent. It is generally exothermic in nature, wherein a large amount of heat is liberated. Due to this heat, the metals produced are in the molten state.
An example of thermite reaction is the reduction of iron (III) oxide by using aluminium powder
Fe₂O₃ sIron III oxide ⁺ 2Al sAluminium powder → 2 Fe lIron + Al₂O₃ sAluminium oxide + Heat
Iron metal is produced when a mixture of iron (III) oxide and aluminium powder is ignited with a magnesium ribbon. The iron, so obtained, is in the molten state due to the large amount of heat liberated in the process. This is used to weld broken pieces of iron.
The above reaction is widely used in thermite welding to join broken pieces of iron.

Answer 33:
Column I Column II
Electrolytic reduction Aluminium, sodium
Reduction with carbon Zinc, iron, tin
Reduction with aluminium Manganese

Answer 34:
(a) Copper is a less reactive metal compared to iron. It reacts very slowly with water. However, steel has less resistance to corrosion, even though it is an alloy of iron. Thus, copper, being very less reactive than steel, is used to make hot water tanks but steel (an alloy of iron) is not.
(b) Most of the metals are reactive towards air. They react with oxygen present in the air to form metal oxides. The metal oxide formation appears on the surface of the metals as a thin layer. This thin layer formation of metal oxide on the metallic surface causes the dull appearance of the metals. Thus, the surface of some metals acquires a dull appearance when exposed to air for a long time.

Answer 35:
(a) Aluminium is a highly reactive metal. It reacts easily with oxygen in the air and forms a layer of aluminium oxide on its surface. This layer is very tough and does not allow air to enter the metal for further reaction. This prevents aluminium from further corrosion. Thus, aluminium articles become unreactive toward air and water and do not corrode easily due to the presence of strong aluminium oxide layer on it. Hence, aluminium is highly resistive to corrosion.
(b) Anodising is a method that involves the formation of tough layer of aluminium oxide on aluminium substances by making it anode in the electrolysis of sulphuric acid. Generally, the formation of aluminium oxide layer on aluminium protects it from corroding further. However, if this oxide layer on aluminium is made thicker (by anodising), it will become a strong coating and will prevent corrosion to the maximum.

Answer 36:
(a) To prevent rusting of iron substances, they are painted frequently. Iron is a reactive metal and it starts corroding in the presence of air (oxygen) and water (or moisture). Iron reacts with oxygen present in the moist air and forms a brown flaky iron oxide (or rust) layer on its surface. This is called rusting. This rusting causes huge damage to iron substances by making them weak. Therefore, an iron grill is painted frequently to prevent corrosion.
(b) Aluminium is more reactive than iron. It reacts easily with oxygen in moist air and forms a layer of aluminium oxide on its surface. This aluminium oxide layer is very strong and does not allow the air to enter the metal for further reaction. This prevents further corrosion of aluminium. On the other hand, the formation of iron oxide layer by iron on reacting with moist air does not prevent the metal. It further allows the reaction between iron and moist air to continue and increases corrosion. Thus, aluminium is a highly resistive metal to corrosion and protects itself against corrosion as compared to iron when exposed to air.

Answer 37:
(a) Aluminium is extracted by electrolytic reduction from molten aluminium oxide.
(b) One of the ores of copper is copper glance. The formula of the ore is Cu₂S.
(c) Calamine, zinc carbonate ZnCO₃, can be extracted by calcination. As zinc is moderately reactive and is placed at the middle of the reactivity series, it can be reduced by carbon. The steps involved in the extraction of zinc are:
1. Concentrated carbonate of zinc is converted to its oxide by calcination. In this process, zinc carbonate ore is strongly heated in the absence of air to produce zinc oxide and carbon dioxide gas.
ZnCO₃(s) →Calcination ZnO(s) + CO₂(g)
2. Zinc oxide is then reduced by coke (carbon). When zinc oxide is heated with coke, carbon acts as a reducing agent and reduces zinc oxide to zinc.
ZnO(s) + C(s) →reduction Zn(s) + CO(g)

Answer 38:
(a) Copper and silver metals occur in nature in free as well as combined state.
(b) One ore of manganese is pyrolusite. This is an oxide ore. Manganese dioxide is the compound present in pyrolusite. Its chemical formula is MnO₂.
(c) If zinc ore forms sulphur dioxide on heating in the presence of air, it should be a sulphide ore, i.e., zinc blende (Zinc sulphide or ZnS).
Two stages involved in the conversion of this concentrated zinc blende to zinc metal are:
1. Roasting: Zinc blende ore is subjected to roasting, i.e., it is heated in the presence of excess air. This converts zinc sulphide ore to zinc oxide. The reaction involved is:
2ZnS(s)+ 3O₂(g)→Surplus of airRoasting
2ZnO(s) + 2SO₂(g)
2. Reduction: Zinc oxide is then reduced by coke (carbon). When zinc oxide is heated with coke, carbon acts as reducing agent and reduces zinc oxide to zinc metal.
ZnO(s) + C(s)    →reduction    Zn(s) +  CO(g)

Answer 39:
Reactivity series depicts the reactivities of metals in decreasing order. It is very helpful in the extraction of metals. The extraction of metals depends on their reactivities.
For extraction purpose, metals in the reactivity series are ordered under three sections:
1. Highly reactive metals
2. Moderately reactive metals
3. Low reactive metals
Depending on the reactivities, different methods are applied for extracting metals from their ores.
Sodium, potassium, calcium, magnesium and aluminium are highly reactive metals and placed at the top of the reactivity series. These metals are extracted by electrolytic reduction of their molten chlorides or oxides because these metals are not reduced by other reducing agents like coke, carbon monoxide etc.
Moderately reactive metals like zinc, iron, lead and copper are placed at the middle of the reactivity series. They are reduced by carbon because carbon is more reactive than these metals and can reduce their metal oxides to metal easily. However, manganese is more reactive than zinc (above zinc in reactivity series); therefore, it cannot be reduced by carbon. It is reduced by a more reactive reducing agent aluminium. Aluminium reduces manganese dioxide to manganese on heating.
Low reactive metals like copper and mercury are placed at the bottom of the reactivity series and are extracted by heating their ores alone. We should note that ores of copper can be extracted by both – reduction with carbon (copper (I) oxide) and heating alone (copper (I) sulphide).
Refer to the following diagram for quick glance of extraction of metals based on their reactivities:

Answer 40:
Sodium, potassium, calcium, magnesium and aluminium are highly reactive metals and are placed at the top of the reactivity series. These metals are extracted by electrolytic reduction of their molten chlorides or oxides because these metals are not reduced by other reducing agents like coke, carbon monoxide etc.
Let us take an example of extraction of sodium metal. Sodium metal is extracted by electrolytic reduction of molten sodium chloride. On passing electricity through molten sodium chloride, decomposition reaction occurs and formation of sodium metal and chlorine gas takes place.
2NaCl(l) →electrolysis 2Na(s) + Cl₂(g)
Molten sodium chloride consists of sodium and chloride ions. The reactions that occurs during electrolysis are:
1. Cathode produces electrons to reduce sodium ions to sodium atoms (or sodium metal) by acting as a reducing agent. Sodium ions are cations; therefore, they get attracted to negatively charged cathode and get deposited there.
Cathode: 2Na⁺ + 2e^– → 2Na Sodium ions Electrons Sodium atoms (from molten NaCl) from cathode (or sodium metal)
2. Chloride ions, being anions, get attracted to positively charged anode. These chloride ions are oxidised to chlorine gas. Chlorine gas is produced at anode.
Anode: 2Cl^– – 2e^– → Cl₂ Chloride ions electrons Chlorine gas (from molten NaCl) to anode

Answer 41:
The oxides of moderately reactive metals like zinc, iron, lead copper, placed in the middle of the reactivity series, are reduced by carbon because carbon is more reactive.
Let us take an example of extraction of zinc from its carbonate ore, i.e., calamine.
The steps involved in the extraction of concentrated calamine ore are:
1. Carbonate of zinc is converted to its oxide by calcination process. In calcination process, zinc carbonate ore is heated strongly in the absence of air to produce zinc oxide and carbon dioxide gas.
ZnCO₃ →Absence of airCalcination ZnO + CO₂Zinc carbonate Zinc Oxide Carbon dioxide(Calamine ore)
2. Zinc oxide is then reduced by coke (carbon). When zinc oxide is heated with coke, carbon acts as a reducing agent and reduces zinc oxide to zinc metal.
ZnO + C →Reduction Zn + COZinc Oxide Coke Zinc metal Carbon monoxide gas (reducing agent).

Answer 42:
The ores of less reactive metals like copper and mercury are placed at the bottom of the reactivity series. Metals are extracted from these ores by heating them alone. We should note that ores of copper can be extracted by reduction with carbon (copper (I) oxide) as well as heating alone (copper (I) sulphide).
Let us explain this by taking the example of extraction of mercury from its cinnabar ore (HgS). Cinnabar is a sulphide ore. On heating the ore, mercury can be extracted. It is a sulphide ore; therefore, it is first heated in the presence of surplus air (roasting). This converts mercury (II) sulphide to mercury (II) oxide.
2HgS + 3O₂ →Surplus of airRoasting 2HgO + 2SO₂
Mercury (II) oxide is then heated to around 300o C. On heating, it gets reduced (decomposes) to mercury metal and oxygen gas is released.
2HgO →Heating 300o CReduction Hg + O₂ Mercury (II) oxide Mercury metal Oxygen gas

Answer 43:
The metals obtained by different reduction processes are usually found to be with some impurities. The process involved in the removal of these impurities from the reduced metals is called purification or refining of metals. There are several refining methods used to purify metals based on the type of metals.
The most widely used method for the refining of impure metals obtained by various reduction processes is electrolytic refining method. Electrolytic refining is a process of purification by electrolysis. Several metals like copper, zinc, tin, lead, nickel, chromium, gold and silver are refined by this process.
Let us explain electrolytic refining process by considering an example of copper metal. The electrolytic refining tank consists of anode, cathode and electrolytic solution. In the refining of copper metal, a bulky piece of impure copper is made anode (attached to positive terminal) and a thin layer of pure copper is made cathode (attached to negative terminal). The acidified copper sulphate solution (copper sulphate solution with dilute sulphuric acid) is taken as electrolytic solution or electrolyte.

When electricity is passed through the cell, impure copper from the anode (as Cu²⁺ ions) melts and travels to the electrolyte. The pure copper metal (Cu²⁺ ions) from the electrolyte moves to the cathode and gets deposited there as pure copper. The amount of copper ions from the anode going to the electrolyte will be equivalent to the amount of copper ions collected at the cathode. This keeps the concentration of the electrolyte constant and proceeds the further reaction. Copper ions, being positively charged, get attracted to the negatively charged cathode and are collected or deposited there.
The copper sulphate electrolyte contains Cu²⁺ and SO₄^2- ions. The reactions that take place at anode and cathode when electricity passed through the electrolytic cell are:
(i) The impure copper atoms from anode lose two electrons to form copper ions and enter the copper sulphate electrolyte.
Anode: Cu – 2e- →Oxidation Cu²⁺
(ii) The copper ions from the copper sulphate electrolyte move to cathode (negatively charged) by gaining two electrons from cathode and get reduced to copper atoms.
Cathode: Cu²⁺ + 2e- →reduction Cu
Thus impure copper atoms, entering copper sulphate electrolyte from anode, get deposited as pure copper atoms at cathode. As the process continues, cathode (pure metal collected) becomes thicker and anode (impure metal) becomes thinner. The metal obtained would be 99.99 percent pure. This pure copper is separated from the cathode later. The impurities are thrown back under the anode as anode mud.​

Exercise : Solution of Questions on page Number : 193

Answer 44
(a) (i) Minerals: Naturally occurring metals or its compounds are called minerals.
(ii) Ore: Ore is a type of mineral from which metal can be extracted profitably and conveniently.
(iii) Gangue: The impurities like sand, mud, rocky substances etc. that are present in an ore are called gangue.(b) An ore usually contains some undesired impurities like sand, mud, rocky substances etc. that are present with the metal. These impurities are called gangue. These impurities are required to be removed before extracting the metal from its ore. Several physical and chemical methods are used to remove these gangue substances from the ore. This process of removing gangue substances from the ore to enhance the concentration (percentage) of metal is called the concentration of the ore.
(c) An ore of copper, other than cuprite, is copper glance. Copper glance is a sulphide ore. The compound present in the ore is copper (I) sulphide. The chemical formula of the ore is Cu₂S.

Answer 45:
When iron (III) oxide and aluminium powder are heated together, aluminium acts as a reducing agent and reduces iron (III) oxide to iron metal. It also gets oxidised to aluminium oxide with the liberation of excess heat. As excess heat is liberated in the reaction, the product, i.e., iron metal is formed in molten state. This reaction is an oxidation-reduction reaction and its chemical equation is:
Fe₂O₃(s) + 2Al(s) →heat 2Fe(l) + Al₂O₃(s) + Excess heat
This reaction is called as thermite reaction. This reaction is widely used to weld cracked machine parts of iron. This is called thermite welding.

Answer 46:
(a) Corrosion is the damage caused to the metal by the chemical reaction of air, water and acids with the surface of the metal. Generally reactive metals corrode easily and non-reactive metals have good resistance to corrosion.
(b) Gold and platinum are two metals that do not corrode easily. These two metal are highly non-reactive; therefore, they have a very high resistance to corrosion.
(c) The corrosion of iron is known as rusting. Iron is a reactive metal and corrodes (rusts) in the presence of air (oxygen) and water (dampness).
(d) Aluminium is a highly reactive metal. It reacts easily with oxygen in the air and forms layer of aluminium oxide on its surface. This aluminium oxide layer is very tough and does not allow the air to enter the metal for further reaction. This prevents further corrosion of aluminium. Therefore, aluminium articles become unreactive towards air and water and do not corrode easily due to the presence of strong aluminium oxide layer over them. This oxide layer on aluminium is made further strong by making it thick by a process called anodising. This prevents corrosion to the maximum. Hence, aluminium becomes highly resistive to corrosion and it is used to make utensils for cooking.

Answer 47:
Iron objects, kept in moist air for a long period of time, react with moist air to form a reddish brown crumbling substance called rust (hydrated iron (III) oxide, Fe₂O₃. X H₂O, where X is the number of moles of water that differs). This corrosion of iron metal by reacting with moist air is called the rusting of iron.
Conditions essential for the rusting of iron:
1. Presence of air (oxygen)
2. Presence of water (moisture)
Let us do an activity to prove that moist air is necessary for the rusting of iron.Experiment: Take three test tubes and place a dirt-free iron nail in each of these test tubes (refer to the figure below). In the first test tube, anhydrous calcium chloride is added and the test tube is closed. In the second test tube, distilled water and a layer of oil is added and the test tube is closed with a cork. In the third test tube, tap water is added. The nail is dipped into water in such a way that a part of it is exposed to the damp air present inside the test tube.

Answer 48:
(a) An alloy is a uniform combination of two or more metals or a metal with a non-metal. It is produced by mixing metals in their molten state in desired quantities. The mixture is then cooled at room temperature. Similarly, an alloy of a metal and a non-metal is prepared by dissolving the non-metal in the molten metal. The mixture is then cooled at room temperature.
(b) Steel is an alloy of iron. It is composed of iron with 0.1 to 1.5 per cent carbon. Iron is not suitable to be used in its pure form because pure iron is very soft and elongates easily when hot. Alloying iron with 0.1 to 1.5 per cent carbon changes the properties of pure iron. This combination is steel that is hard and strong in nature. Steel rusts too but not as easily as iron.
(c) Brass is an alloy of copper and zinc. Composition of brass is copper (80 percent) and zinc (20 percent). Brass is used for making vessels and scientific instruments (e.g.microscope).

Answer 49:
(a) Aluminium and zinc are two metals that resist corrosion due to the formation of a thin, hard and impervious layer of oxide on their surface. Aluminium and zinc form tough layers of aluminium oxide and zinc oxide by reacting with air.
(b) Five methods of preventing rusting of iron are:
By polishing the surface of iron with paint
By applying oil or grease on the surface of iron
By coating a thin layer of zinc on the iron metal by the process called galvanisation
By coating other metals like tin coating and chromium coating
By alloying with other metals (chromium and nickel) to form stainless steel, which does not corrode
(c) The constituent elements present in stainless steel are iron, nickel and chromium.
Special properties of stainless steel are:
It is hard and strong.
It does not corrode (does not rust).
These properties make it suitable for making utensils for cooking.

Answer 50:
(a) An alloy of copper is bronze. The constituent elements of bronze are copper and tin.
The composition of bronze is 90 percent copper and 10 percent tin. This alloy of copper is very strong and prevents corrosion.
Bronze is used in the manufacturing of statues, medals, cooking vessels etc.
(b) Copper object, staying in damp air for a long time, reacts with carbon dioxide and moisture (water) in air slowly to form green layer of basic copper carbonate CuCO₃.Cu(OH)₂ on the outside area of the object. This process is known as corrosion. Copper is very low in its reactivity; therefore, corrosion of copper also occurs slowly.

Answer 51:
(a) The regular method used to prevent rusting of iron objects is painting the surfaces of iron objects. Rusting takes place in the presence of both air and water. Thus, when a layer of paint is applied to the surface of an iron object, it prevents the contact of air and moisture with the iron surface and avoids the rusting of iron objects.
(b) Alloys of copper, brass (alloy of copper and zinc) and bronze (alloy of copper and tin) are very poor conductors of electricity. However, copper is an excellent conductor of electricity; therefore, it is used in electrical wiring.
(c) An alloy of gold with copper or silver (Cu and Ag are mixed with gold to make it harder) is called 22 carat gold. The value refers to 22 parts of pure gold alloyed with two parts of either silver or copper. 22 carat gold is used for making jewellery.

Answer 52:
(a) When zinc carbonate is heated in the absence of air, it is converted to zinc oxide with the evolution of carbon dioxide gas. This is one of the methods used to convert concentrated metal carbonates to metal oxides during extraction of metals. This method is called calcination. The given zinc carbonate is nothing but calamine ore of zinc, which gets converted to zinc oxide on calcination.
ZnCO₃ →Calcination ZnO + CO₂Zinc carbonate Zinc oxide carbon dioxide(Calamine ore)
(b) When a mixture of Cu₂O and Cu₂S is heated, they react together to give copper metal and sulphur dioxide gas. This is one of the methods used to reduce sulphide ore of less reactive copper to copper metal. Copper glance, Cu₂S, is roasted in the presence of air to get converted to Cu₂O. Cu₂O then reacts with non-oxidised Cu₂S ore in the absence of air to form copper metal.

2Cu₂O + Cu₂S →Heated 6Cu + SO₂ Copper (I) Copper (I) Copper Sulphur oxide sulphide metal dioxide.

Answer 53:
(a) Aluminium (Al) can be used as a reducing agent for the reduction of a metal oxide. This is generally used for reducing metal oxides such as manganese dioxide (MnO₂).
(b) If an aqueous solution of sodium chloride is used in electrolysis, sodium metal, formed at cathode, will immediately react with water in the aqueous solution to form sodium hydroxide because sodium is a highly reactive metal. Hence, it is important to use molten sodium chloride and not its aqueous solution in electrolytic extraction.

Answer 54:
The process of electrolysis is used in electrolytic refining. This is the most widely used method for the refining of impure metals. Several metals like copper, zinc, tin, lead, nickel, chromium, gold, silver are refined by this process.
Electrolytic refining of copper:
An electrolytic refining tank consists of an anode, a cathode and an electrolyte (acidified copper sulphate solution). A thick rod of an impure metal is made the anode and attached to the positive terminal. A thin rod of a pure metal is made the cathode and attached to the negative terminal. When electricity is passed through the cell, impure metal from the anode gets dissolved in the electrolyte. The metal ions from the electrolyte move to the cathode and get deposited there as pure metal. While the soluble impurities dissolve in the electrolyte, the insoluble ones deposit under the anode as anode mud.

When electricity is passed through the electrolytic cell, following reactions take place at the anode and cathode:
(i) Impure copper atoms from the anode lose two electrons to form copper ions and enter copper sulphate electrolyte.
Anode: Cu – 2e^– →Oxidation Cu²⁺ (impure metal) Electrons (copper ions enters electrolyte) (from anode)
(ii) Copper ions from the copper sulphate electrolyte move to the cathode (negatively charged) by gaining two electrons from the cathode. Thus, they get reduced to copper atoms.
Cathode: Cu²⁺ + 2e^– →reduction Cu Copper ions Electrons Pure copper metal(from electrolyte) (from cathode) (deposited at cathode)
As the process continues, the cathode (pure metal collected) progressively becomes thicker and anode (impure metal) keeps getting thinner. The metal obtained is 99.99 percent pure.

Answer 55:
(a) Aluminium oxide is electrolysed in molten state to obtain aluminium metal. Oxygen gas is evolved during this process.
The equation for this decomposition is:
2Al₂O₃ (l) →Electrolysis 4Al (l) + 3O₂ (g)Aluminium Aluminium Oxygen oxide
(b) ​Sodium chloride is electrolysed in molten state to obtain sodium metal. Chlorine gas is evolved during this process.
The equation for this decomposition is:
2NaCl (l) →Electrolysis 2Na (s) + Cl₂ (g)Sodium chloride Sodium Chlorine
(c) Carbon dioxide (CO₂) gas is produced when calamine ore is calcined.
ZnCO₃ (s) →Calcination ZnO (s) + CO₂ (g)Zinc carbonate Zinc oxide Carbon dioxide (Calamine ore)
(d) Sulphur dioxide gas is evolved when cinnabar ore is roasted.
2HgS(s) + 3O₂ (g) →Roasting 2HgO (s) + 2SO₂ (g) Mercury (II) Oxygen Mercury (II) Sulphur sulphide oxide dioxide

Answer 56:
(a) Gold (Au) and silver (Ag) are found in nature in free state. This is because they are non-reactive metals.
(b) Sodium (Na) and magnesium (Mg) are always found in combined state. This is because they are highly reactive and their oxides are highly stable.
(c) Haematite ore contains iron (III) oxide. Its chemical formula is Fe₂O₃.

Answer 57:
(a) The differences between a mineral and an ore are listed below:
Mineral Ore
1. Naturally occurring metals or their compounds are called minerals. Minerals containing good quantity of metals that can be profitably mined are called ores.
2. Minerals may or may not contain metals in large percentages. Ores always contain metals in large percentages.
3. Minerals may or may nor contain objectionable impurities. Ores do not contain objectionable impurities.
4. All minerals are not ores. All ores are minerals.
(b) Mercury is extracted from cinnabar ore. It is the sulphide ore of mercury and its chemical formula is HgS. The name of the compound present in cinnabar is mercury (II) sulphide. It is a sulphide ore; therefore, it is first heated in the presence of surplus air (roasting). This converts mercury (II) sulphide to mercury (II) oxide.
2HgS + 3O₂ →surplus airRoasting 2HgO + 2SO₂
Mercury (II) oxide is then heated again to around 300o C. On heating, it gets reduced to mercury.
2HgO →300o C Heating 2Hg + O₂

(c) The ore of sodium is rock salt. The sodium compound present in this ore is sodium chloride. The chemical formula of the ore is NaCl.
(d) Sodium is extracted by electrolytic reduction of molten sodium chloride. On passing electricity through molten sodium chloride, decomposition occurs and sodium metal and chlorine gas are formed.
2NaCl(l) →Electrolysis 2Na(s) + Cl₂(g)
Molten sodium chloride contains sodium and chloride ions. The reactions that occur during electrolysis are:
1. The cathode produces electrons to reduce sodium ions to sodium atoms (or sodium metal) by acting as reducing agent. Sodium ions are cations; therefore, they are attracted to the negatively-charged cathode and get deposited there.
Cathode: 2Na⁺ + 2e^– → 2Na
2. Chloride ions are anions; therefore they are attracted to the positively-charged anode. These chloride ions are oxidised to chlorine gas. Chlorine gas is produced at the anode.
Anode: 2C^l- – 2e^– → Cl₂ ​
(e) Potassium, calcium and aluminium are highly reactive metals like sodium and are also placed on the top of the reactivity series. These metals are not reduced by other reducing agents such as coke, carbon monoxide etc.​ Like sodium, these metals are also extracted by electrolytic reduction of their molten chlorides or oxides.

Answer 58:
(a) The metal extracted from hematite ore is iron. Hematite ore contains iron (III) oxide (Fe₂O₃). This iron oxide is extracted by heating it with aluminium. Aluminium acts as a reducing agent and reduces iron (III) oxide to iron.
(b) Bauxite is an ore of aluminium. The aluminium compound present in this ore is aluminium oxide. Its chemical formula is Al₂O₃.2H₂O.(c) ​ Aluminium is extracted by electrolytic reduction of its molten oxide. Aluminium is a highly reactive metal and it is placed at the top of the reactivity series. This cannot be reduced by other reducing agents such as coke, carbon monoxide etc.
On passing electricity through molten aluminium oxide, decomposition reaction occurs and formation of aluminium metal and oxygen gas takes place.
2Al₂O₃(l)    →Electrolysis    4Al(s)  + 3O₂(g)
Molten aluminium oxide consists of aluminium and oxide ions. The reactions that occur during electrolysis are:
1. Cathode produces electrons to reduce aluminium ions to aluminium atoms (or aluminiummetal) by acting as reducing agent. Aluminium ions are cations; therefore, they get attracted to negatively charged cathode and get deposited there.
Cathode: Al₃+ +   3e-   →   Al
2. Oxide ions are anions; therefore, they get attracted to positively charged anode. These oxide ions are oxidised to oxygen gas. Oxygen gas is produced at anode.
Anode:             2O₂^– –  4e-  →  O₂ 
(d) Aluminium metal is produced at cathode. During electrolysis, cathode produces electrons to reduce aluminium ions into aluminium atoms (or aluminium metal) by acting as reducing agent.  Aluminium ions are cations; therefore, they get attracted to negatively charged cathode and get deposited there.
Cathode:              Al₃+  +  3e^–   →    Al

(e) Oxygen gas is produced during the extraction of aluminium. This oxygen gas is produced at anode. During electrolysis, aluminium atoms are deposited at cathode, whereas oxide ions, being anions, get attracted to positively charged anode. These oxide ions are oxidised to oxygen gas. Oxygen gas is produced at anode.
Anode:             2O₂–^–  4e^–   →  O₂

Exercise : Solution of Questions on page Number : 194

Answer 59:
(a) Aluminium metal is extracted from bauxite ore. The aluminium compound present in this ore is aluminium oxide. The chemical formula of the ore is Al₂O₃.2H₂O.
(b) Hematite is an ore of iron. Iron compound present in hematite ore is iron (III) oxide. The formula of the ore is Fe2O3.
(c) Zinc blende (ZnS) is the sulphide ore of zinc. The extraction of zinc from zinc blende involves two steps. First, the concentrated zinc blende is converted to its oxide (by roasting). After this, the oxide is reduced to zinc metal. The reactions for the two processes are:
1. Roasting: Zinc blende is subjected to roasting, i.e. it is heated in the presence of excess air. This converts zinc sulphide ore to zinc oxide.
The reaction involved is:
2ZnS + 3O₂ →Surplus air Roasting ​2ZnO +2SO₂
2. Reduction: Zinc oxide is then reduced by coke (carbon). When zinc oxide is heated with coke, carbon acts as a reducing agent and reduces zinc oxide to zinc metal.
ZnO +C →Reduction Zn + CO
(d) The galvanised iron-zinc oxide layer coating on iron objects prevents zinc and iron under it​ from corrosion. This happens because zinc is more reactive than iron. If the zinc layer is broken,​ zinc, being more reactive, gets oxidised before iron and prevents its corrosion.
(e) Aluminium is a common metal that is highly resistant to corrosion because it is a highly reactive metal. It reacts easily with oxygen in air and forms a layer of aluminium oxide on its surface. This aluminium oxide layer is very tough and does not allow air to enter the metal for further reaction, thus preventing further corrosion of aluminium.

Answer 60:
(a) The metal extracted from the ore rock salt is sodium. The sodium compound present in this ore is sodium chloride. The chemical formula of the ore is NaCl.
(b) The two ores of zinc are calamine ore and zinc blende. The chemical compound present in calamine is zinc carbonate (carbonate ore) and its chemical formula is ZnCO₃. The chemical compound present in zinc blende is zinc sulphide (sulphide ore) and its chemical formula is ZnS .
(c) Cinnabar is a sulphide ore of mercury. The name of the compound present in the cinnabar ore is mercury (II) sulphide. Its chemical formula is HgS. Mercury is a less reactive metal and it can be extracted from its sulphide ore cinnabar by heating it in air alone.
1. It is first heated in the presence of surplus air (roasting process). This converts mercury (II) sulphide to mercury (II) oxide.
2HgS + 3O₂ →Surplus airRoasting 2HgO + 2SO₂
2. Mercury (II) oxide, so formed, is heated to around 300oC and it gets reduced to mercury metal.
2HgO →300^oC Heating 2Hg⁺O₂
(d) In electrolytic refining of a metal, the electrolytic refining tank consists of:
Anode: A bulky piece of impure metal (attached to positive terminal)
Cathode: A thin layer of pure metal (attached to negative terminal)
Electrolyte: Salt solution of the metal, which is being refined, is taken as the electrolytic solution or electrolyte.
When electricity is passed through the cell, impure metal from the anode melts and goes into the electrolyte. The pure metal from the electrolyte moves to the cathode and gets deposited there as pure metal. The impurities that are soluble dissolve in electrolyte and insoluble impurities deposit under anode as anode mud.
(e) Five metals that can be purified by electrolytic refining method are copper, zinc, chromium, lead and nickel.

Answer 61:
(a) Zinc metal is extracted from calamine ore. Calamine ore is a carbonate ore. The compound present in it is zinc carbonate. Its formula is ZnCO₃.
(b) The ore of mercury is cinnabar. Cinnabar is a sulphide ore. The compound present in it is mercury (II) sulphide. Its chemical formula is HgS.
(c) The sulphide ore of copper is copper glance. The compound present in the ore is copper (I) sulphide. Its formula is Cu₂S. Copper is a less reactive metal; therefore, it is placed at the bottom in the reactivity series. Copper is extracted by heating its sulphide ore alone.
Two steps involved in the extraction of copper metal from concentrated copper glance ore are:
1. Roasting: Copper glance, being a sulphide ore, is heated in the presence of air. Copper (I) sulphide is converted to copper (I) oxide.
2Cu₂S(s)+ 3O₂(g) →Surplus airRoasting 2Cu₂O(s) + 2SO₂(g)
2. Copper (I) oxide, so formed, reacts with non-oxidised copper (I) sulphide ore in the absence of air to form copper metal. When the mixture of Cu₂O and Cu₂S is heated, they react together to give copper metal and sulphur dioxide gas.
2Cu₂O(s) + Cu₂S(s) →Heat 6Cu(s)+ SO₂(g)
(d) A uniform combination of two or more metals or a metal with a non-metal is called an alloy. Alloys are produced by mixing metals in their molten state in desired quantities and allowing the solution to cool at the room temperature. Similarly, an alloy of a metal and non-metal is prepared by dissolving the non-metal in the molten metal and allowing the solution to cool at the room temperature.
Examples: Steel is an alloy of iron. The composition of steel is iron with 0.1 to 1.5 % carbon.
Brass is an alloy of copper and zinc. Its composition is 80 percent copper and 20 percent zinc.
(e) The properties of alloys are different from those of the constituent elements :
1. Alloys have higher strength than their constituting metals. Example: Steel is an alloy of iron with carbon and it has higher strength than iron.
2. Alloys are harder than their constituting metals. Example: Magnalium is an alloy of aluminium and magnesium and it is harder than aluminium.
3. Alloys have high resistance to corrosion than their constituting metals.​ Example: Stainless steel is an alloy of iron, nickel and chromium, and it does not corrode at all, whereas iron rusts easily.
4. Alloys have lesser melting points than their constituting metals.​ ​Example: Solder an alloy of tin and lead and it has a very low melting point, which is less than its constituting metals.
5. Alloys have low electrical conduction than their constituting metals.​ ​Example: Copper is an excellent conductor of electricity but brass (alloy of copper and zinc) and bronze (alloy of copper and tin) are poor conductors of electricity.

Answer 62:
(d) Pyrolusite
​Pyrolusite is an ore of manganese and the compound is manganese dioxide (textrm{MnO₂).

Answer 63:
(c) Haematite.
Haematite is an iron ore and the compound is iron (III) oxide (Fe₂O₃).

Answer 64:
(c) Al
Aluminium can be extracted from bauxite. Bauxite is an ore of aluminium and the compound is aluminium oxide (Al₂O₃.2H₂O).

Answer 65:
(d) mercury and copper
Both mercury and copper are less reactive metals and are placed low in the reactivity series. Hence, they can be extracted by heating their sulphides in air and further reducing their oxides by heating.

Answer 66:
(c) aluminium
Aluminium is resistant to corrosion due to the formation of a thin oxide layer (aluminium oxide or Al₂O₃). This prevents further corrosion by creating a strong protective layer over the surface of the metal.

Answer 67:
(a) calamine
Calamine is an ore of zinc and the compound is zinc carbonate (ZnCO₃).

Answer 68:
(c) bauxite
Bauxite is one of the major ores of aluminium. Its compound is aluminium oxide (Al₂O₃.2H₂O).

Answer 69:
(d) magnesium and aluminium
This is because magnesium and aluminium are highly reactive metals and are placed high in the reactivity series. This is also due to the fact that their oxides are very stable and cannot be reduced easily.

Answer 70:
(b) Cr and Ni
Stainless steel is an alloy of iron, chromium and nickel. It is extremely strong and tough and does not corrode at all.

Answer 71:
(c) basic copper carbonate
Copper reacts slowly with water and carbon dioxide in the atmosphere to form copper carbonate. This gives a green colour coating to its surface.

Answer 72:
(d) zinc amalgam
Generally, alloys containing mercury as one of its constituents are known as amalgam. Zinc amalgam is an alloy of zinc and liquid mercury.

Answer 73:
(b) cinnabar
Cinnabar is an important ore of mercury. Its compound is mercury (II) sulphide (HgS).

Answer 74:
(d) Zinc.
Calamine is an ore of zinc and its compound is zinc carbonate (ZnCO₃).

Exercise : Solution of Questions on page Number : 195

Answer 75:
(d) Au and Ag
Gold (Au) and silver (Ag) are highly non-reactive. Hence, they are available in native state in nature and do not react with oxygen or any other element in the atmosphere.

Answer 76:
(c) Fe₂O₃⁺ Al
In this thermite reaction, iron (III) oxide and aluminium powder are combined and heated. Iron oxide gets reduced to iron by the action of reducing agent aluminium and produces excess heat. The molten iron produced is poured in the middle of the broken pieces of irons that are fixed mutually.

Answer 77:
(c) Steel
Steel is an alloy that contains a non-metal carbon as one of its constituents. It consists of iron with carbon (0.1 to 1.5 %).

Answer 78:
(a) at cathode
In electrolytic refining, pure metal is always deposited at the cathode. The impure metal is made anode (positive terminal) and a thin rod of pure metal is made cathode (negative terminal). The salt of the metal is made electrolyte in the cell. When electricity passed through the cell, the impure metal dissolves in the electrolytic solution. The pure metal from the electrolytic solutions moves and gets deposited at the cathode.

Answer 79:
(d) Iron
Iron can be obtained from hematite ore. Hematite ore contains the compound iron (III) oxide (Fe₂O₃).

Answer 80:
(d) Zn and Cu
Brass is an alloy of copper and zinc. It comprises of 80 percent copper and 20 percent zinc.

Answer 81:
(c) mercury
An amalgam is an alloy of mercury with one or more metals. The combination of sodium with liquid mercury is called sodium amalgam. Amalgam of mercury with gold, silver or zinc is widely used for dental fillings.

Answer 82:
(d) aluminium
There are some metals that cannot be satisfactorily reduced by carbon. In such cases, aluminium is used as reducing agent, e.g., manganese.

Answer 83:
(d) Hg
Mercury is a low reactive metal. Thus, it can be extracted from its ore cinnabar, HgS, by heating it in air.

Answer 84:
(c) zinc
Galvanisation is a process that involves dipping of iron objects into melted zinc. This gives a thin coating of zinc layer on the iron object that protects it from corrosion. Zinc, being a highly reactive metal, forms a thin layer of zinc oxide, which prevents iron from getting exposed to the atmospheric air.

Answer 85:
(c) Na and Mg
Sodium (Na) and magnesium (Mg) are highly reactive metals. They are not easily reduced by carbon and aluminium. Thus, they are extracted by electrolytic reduction or electrolysis of their molten chlorides (sodium chloride, NaCl, and magnesium chloride, MgCl₂).

Answer 86:
(b) Na
Rock salt is a chloride ore of sodium. The name of the compound in the ore is sodium chloride with chemical formula NaCl.

Answer 87:
(c) sulphide
Silver reacts with hydrogen sulphide gas in the air and forms a think black layer of silver sulphide (Ag₂S) on it. Silver jewellery or ornaments become dull because of the formation of silver sulphide coating on their surfaces.

Answer 88:
(b) roasting
Sulphide ores are transformed into oxides by the process of roasting. In this process, concentrated ore is heated in the presence of surplus air. Example: Zinc blende, ZnS, a sulphide ore of zinc, is roasted in the presence of air. On roasting​, zinc sulphide gets transformed into zinc oxide.

Answer 89:
(b) manganese
Manganese is extracted from its oxide ore, pyrolusite. The name of the compound in the ore is manganese dioxide having chemical formula MnO₂.

Answer 90:
(c) calcination
Calamine (ZnCO₃, zinc carbonate) is a carbonate ore of zinc. Carbonate ores are converted to metal oxides by calcination (heating in the absence of air). When calamine ore (zinc carbonate) is heated in the absence of air, it is converted into zinc oxide.

Answer 91:
(a) roasting
Zinc blende (zinc sulphide or ZnS) is a sulphide ore of zinc. Sulphide ores are converted to metal oxides by roasting (heating in the presence of air). When zinc blende is heated in the presence of surplus air, it is converted into zinc oxide.

Answer 92:
(a) Element A is sodium and element B is chlorine.
Sodium is kept under kerosene because it is highly reactive. Element with atomic number 17 is chlorine. Thus, element A is sodium and element B is chlorine.
(b) When element A, sodium, reacts with element B, chlorine, it forms a product C, sodium chloride, NaCl.
2Na + Cl₂ →2NaCl
When aqueous solution of sodium chloride is electrolysed, compound D, sodium hydroxide (NaOH), is formed along with the evolution of hydrogen and chlorine gases.
NaCl(aq) →electrolysis NaOH(s) + H₂(g) + Cl₂(g)
(c) Compound C is sodium chloride. It has no action on litmus solution. Because sodium chloride is a salt, it is neutral in nature and does not show any action with litmus solution.
(d) Element B is chlorine. It is in gaseous state at room temperature.
(e) The element E with atomic number 5 is boron. When element B, chlorine, reacts with element E, boron, it forms a compound boron trichloride. The formula of the compound formed is BCl₃.
2B+3Cl₂ →2BCl_3.

Answer 93:
(a) The metal is mercury and its chemical symbol is Hg.
(b) Sulphide ore of mercury is cinnabar and its chemical formula is HgS (Mercury (II) sulphide).
(c) Mercury is a less reactive metal. Its ore cinnabar, HgS, is a sulphide ore. On heating the sulphide ore, mercury can be extracted. It is a sulphide ore; therefore, it is first heated with air (roasting process). This converts mercury (II) sulphide to mercury (II) oxide.
2HgS +3O₂ → 2HgO + 2SO₂
Mercury (II) oxide, thus formed, is heated to around 300oC and it gets reduced to mercury.
2HgO → 2Hg + O₂
(d) A common device wherein mercury is used is thermometer.
(e) No, mercury cannot displace copper from its salt solution. Mercury is less reactive than copper and is placed below it in the reactivity series.

Exercise : Solution of Questions on page Number : 196

Answer 95:
(a)The carbon electrode acting as anode (positively charged) is burnt away.
(b) In the electrolysis of molten aluminium oxide using carbon electrodes, the pure metal is formed at the cathode (negatively-charged electrode) and oxygen is formed at the anode (positively-charged electrode). This oxygen reacts with positively-charged carbon electrode and produces carbon dioxide gas. Due to this reaction between oxygen and carbon electrode (anode), the carbon electrode burns away gradually and has to be replaced.

Answer 96:
(a) Metal X is aluminium and metal Y is zinc.
Metal X or aluminium is resistant to corrosion and is produced by electrolysis of molten aluminium oxide. Aluminium is used in thermite welding.
Metal Y or zinc is also resistant to corrosion and is produced by reduction of zinc oxide with carbon (reducing agent). Zinc is widely used in making cathodes of ordinary dry cells.
(b) X (aluminium) is more reactive than Y (zinc). Aluminium is placed above zinc in the reactivity series.
(c) One ore of metal X (aluminium) is bauxite ore. The chemical formula of bauxite ore is Al₂O₃.2H₂O.
(d) One ore of metal Y (zinc) is calamine ore. The chemical formula of calamine ore is ZnCO₃.
(e) One alloy of metal X (aluminium) is magnalium, which consists of aluminium and magnesium. One alloy of metal Y (zinc) is brass, which consists of zinc and copper.

Answer 97:
(a) Metal A is silver. Silver becomes black in the presence of hydrogen sulphide gas in air. Silver reacts with hydrogen sulphide gas in air and forms a thin black layer of silver sulphide (Ag₂S) on it. Therefore, silver jewellery or ornaments become dull due to the formation of silver sulphide coating on their surfaces. Silver is the best conductor of electricity.
(b) Metal C is copper. When copper is kept in moist air, it slowly reacts with carbon dioxide and moisture (water) in the air to form a green layer of basic copper carbonate (CuCO₃.Cu(OH)₂). This basic copper carbonate is a combination of copper carbonate and copper hydroxide. After silver, copper is the next best conductor of electricity.
(c) Substance B is silver sulphide (Ag₂S) .
(d) Substance D is basic copper carbonate (CuCO₃.Cu(OH)₂).
(e) Dilute acid solution can be used to remove the green layer on copper. This acid solution dissolves the green layer of basic copper carbonate present on corroded copper. This helps copper to regain its shine.

Answer 98:
Metal P is Zn (zinc), Q is Sn (tin), R is Pb (lead) and S is Fe (iron).
We arrive to the following conclusion:
Metal P (zinc) is used to form a thin layer on metal S (iron). The process of thin coating of zinc layer on iron objects is called galvanisation. This thin coating of zinc layer on iron objects protects it from corrosion (zinc is a highly reactive metal. It does not rust even in moisture because it forms a thin coat of zinc oxide on reacting with air).
Metal Q (tin) is used for electroplating tiffin boxes made of metal S (iron). This tin coating prevents the corrosion of iron. However, tin coating provides only outside protection.
Metal R (lead) is used in making car batteries. Metal Q (tin) and metal R (lead) are combined together to form an alloy called solder.

Answer 99:
(a) Metal X is manganese.
Manganese dioxide, MnO₂ (black in colour), is used as a catalyst in the preparation of oxygen gas from potassium chlorate. Manganese dioxide is also used in ordinary dry cells. Manganese is a reactive metal; therefore, manganese dioxide cannot be reduced satisfactorily with carbon to form manganese metal.
(b)The metal oxide is manganese dioxide, MnO₂.
(c) Manganese dioxide, MnO₂, cannot be reduced satisfactorily with carbon to form manganese metal. Manganese is comparatively more reactive; therefore, aluminium is used in place of carbon as a reducing agent.
(d) Iron can also be extracted when aluminium is used as a reducing agent. This reaction is called thermite reaction. In this reaction, iron (III) oxide is reduced by with aluminium powder to give iron and aluminium oxide. This reaction is used for welding broken railway tracks.

Answer 100:
Metals X and Y are gold and silver, respectively. They can be recovered from the anode mud that is left behind after the electrolytic refining of copper metal. The coins made of metal X (gold) look new even after several years of use because gold is the least reactive metal and it does not react with air, water, acids, alkalis etc. On the other hand, coins made of metal Y (silver) lose their shine gradually and get blackened soon because silver reacts with hydrogen sulphide gas in the air and forms a thin black layer of silver sulphide (Ag₂S) on it.
When metal X (gold) is alloyed with a small amount of metal Y (silver), it becomes hard and suitable for making ornaments. Pure gold is very soft and cannot be used for making ornaments. However, when it is mixed with silver, it becomes hard and suitable for making ornaments.
The colour of metal X (gold) is yellow.