CBSE - Metals and Non-metals

Answer: Mercury

Sodium  can be easily cut with a knife

Silver is the best conductor of heat.

Mercury and Lead are poor conductor of heat

Malleable:Substances that can be beaten into thin sheets are called malleable. For example, most of the metals are malleable.
Ductile: Substances that can be drawn into thin wires are called ductile. For example, most of the metals are ductile.

Sodium is high reactive element. If it is kept in open it can explosively react with oxygen to catch fire. Hence to prevent accidental damage sodium is immersed in kerosene oil.

(i) 3Fe (s) + 4H₂O (g) → Fe₃O₄ (aq) + 4H₂ (g)

(ii) Ca (s) + 2H₂O (l) → Ca(OH)₂ (aq) + H₂ (g) + Heat
     2K (s) + 2H₂O (l) → 2KOH (aq) + H₂ (g) + Heat

Solution:

A + FeSO₄ → No reaction, i.e., A is less reactive than iron

A + CuSO₄ → Displacement, i.e., A is more reactive than copper

B + FeSO₄ → Displacement, i.e., B is more reactive than iron

B + ZnSO₄ → No reaction, i.e., B is less reactive than zinc

C + FeSO₄ → No reaction, i.e., C is less reactive than iron

C + CuSO₄ → No reaction, i.e., C is less reactive than copper

C + ZnSO₄ → No reaction, i.e., C is less reactive than zinc

C + AgNO₃ → Displacement, i.e., C is more reactive than silver

D + FeSO₄/CuSO₄/ZnSO₄/AgNO₃ → No reaction, i.e., D is less reactive than iron, copper, zinc, and silver

(i) B is most reactive metal.
(ii) B will displace copper from copper sulphate.
(iii) Arrangement of metals in the order of decreasing reactivity B>A>C>D.

Hydrogen gas is evolved when dilute hydrochloric acid is added to a reactive metal.

When iron reacts with dilute H₂SO₄, iron (II) sulphate with the evolution of hydrogen gas is formed.

Fe (s) + H₂SO₄ (aq) → FeSO₄(aq) + H₂ (g) 

When zinc is added to iron (II) sulphate then it will displace the iron from iron sulphate solution as shown in the following chemical reaction.

Zn (s) + FeSO₄ (aq) → ZnSO₄ (aq) + Fe (s)

(i) The representation of elements with valence electrons as dots around the elements is referred to as electron-dot structure for elements.

(ii)

(iii) The ions present in Na2O are Na+ and O2- ions and in MgO are Mg2+ and O2- ions.

Ionic compounds have strong electrostatic forces of attraction between the ions. Therefore, it requires a lot of energy to overcome these forces. That is why ionic compounds have high melting points.

(i) Mineral: The naturally occurring compounds of elements are known as Mineral.
(ii) Ore: Minerals from which metals can be extracted profitably are known as ores.
(iii) Gangue: The impurities present in the ore such as sand, rocks etc are non as gangue.

The metals at the bottom of the reactivity series are mostly found in free state. For example: gold, silver, and platinum.

The chemical process used for obtaining a metal from its oxide is reduction. In this process, metal oxides are reduced by using suitable reducing agents such as carbon or by highly reactive metals to displace the metals from their oxides.

For example, zinc oxide is reduced to metallic zinc by heating with carbon.



Manganese dioxide is reduced to manganese by treatingit with aluminium powder. In this case, aluminium displaces manganese from its oxide.



Oxides of more reactive metals are reduced by electrolysis.

Answer:

More reactive a metal is, more likely it is to be corroded. Therefore, less reactive metals are less likely to get corroded. This is why gold plating provides high resistance to corrosion.
Metals which have low reactivity such as silver, gold does not corrode easily.

An alloy is the homogeneous mixture of two or more metals or metals and non metals. For example brass is an alloy of copper and zinc.

Which of the following pairs will give displacement reactions?
(a) NaCl solution and copper metal
(b) MgCl₂ solution and aluminium metal
(c) FeSO₄ solution and silver metal
(d) AgNO₃ solution and copper metal.

Answer (d) AgNO₃ solution and copper metal.

Which of the following methods is suitable for preventing an iron frying pan from rusting?
(a) Applying grease
(b) Applying paint
(c) Applying a coating of zinc
(d) all of the above.

Answer (c) Applying a coating of zinc

An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be
(a) calcium
(b) carbon
(c) silicon
(d) iron

Answer (a) calcium

Food cans are coated with tin and not with zinc because
(a) zinc is costlier than tin.
(b) zinc has a higher melting point than tin.
(c) zinc is more reactive than tin.
(d) zinc is less reactive than tin.

Answer (c) zinc is more reactive than tin.

(a) With the hammer, we can beat the sample and if it can be beaten into thin sheets (that is, it is malleable), then it is a metal otherwise a non-metal. Similarly, we can use the battery, bulb, wires, and a switch to set up a circuit with the sample. If the sample conducts electricity, then it is a metal otherwise a non-metal.

(b) The above tests are useful in distinguishing between metals and non-metals as these are based on the physical properties. No chemical reactions are involved in these tests.

Those oxides that behave as both acidic and basic oxides are called amphoteric oxides.
Examples: aluminium oxide (Al₂O₃), zinc oxide (ZnO)

Iron and aluminium will displace hydrogen from dilute acids as they more reactive then hydrogen. Mercury and copper cannot displace hydrogen from dilute acids as they are less reactive than hydrogen.

In the electrolytic refining of a metal M:
Anode → Impure metal M
Cathode → Thin strip of pure metal M
Electrolyte → Solution of salt of the metal M

(a)

(i) There will be no action on dry litmus paper.

(ii) The colour of litmus paper will turn red because sulphur is a non-metal and the oxides of non-metal are acidic in nature.
(b) S (s) + O₂(g) → SO₂ (g)

Two ways to prevent the rusting of iron are:
→ Oiling, greasing, or painting: By applying oil, grease, or paint, the surface becomes water proof and the moisture and oxygen present in the air cannot come into direct contact with iron. Hence, rusting is prevented.
→ Galvanisation:An iron article is coated with a layer of zinc metal, which prevents the iron to come in contact with oxygen and moisture. Hence, rusting is prevented.

When non-metals are combined with oxygen then neutral or acidic oxides are formed. Examples of acidic oxides are NO₂, SO₂ and examples of neutral oxides are NO, CO etc.

(a) Platinum, gold, and silver are used to make jewellery because they are very lustrous. Also, they are very less reactive and do not corrode easily.

(b) Sodium, potassium, and lithium are very reactive metals and react very vigorously with air as well as water.Therefore, they are kept immersed in kerosene oil in order to prevent their contact with air and moisture.

(c) Though aluminium is a highly reactive metal, it is resistant to corrosion. This is because aluminium reacts with oxygen present in air to form a thin layer of aluminium oxide. This oxide layer is very stable and prevents further reaction of aluminium with oxygen. Also, it is light in weight and a good conductor of heat. Hence, it is used to make cooking utensils.

(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction because metals can be easily extracted from their oxides rather than from their carbonates and sulphides.

Copper reacts with moist carbon dioxide in air to form copper carbonate and as a result, copper vessel loses its shiny brown surface forming a green layer of copper carbonate. The citric acid present in the lemon or tamarind neutralises the basis copper carbonate and dissolves the layer. That is why, tarnished copper vessels are cleaned with lemon or tamarind juice to give the surface of the copper vessel its characteristic lustre.

Metal	Non Metals
Metals are electropositive.	Non-metals are electronegative.
They react with oxygen to form basic oxides. 4Na + O2 -> 2Na2O These have ionic bonds	They react with oxygen to form acidic or neutral oxides. C + O2 -> CO2 These have covalent bonds.
They react with water to form oxides and hydroxides. Some metals react with cold water, some with hot water, and some with steam. 4Na + O2 -> 2NaOH + H2	They do not react with water.
They react with dilute acids to form a salt and evolve hydrogen gas. However, Cu, Ag, Au, Pt, Hg do not react.	They do not react with dilute acids. These are not capable of replacing hydrogen.
They react with the salt solution of metals. Depending on their reactivity, displacement reaction can occur. CuSO4 + Zn -> ZnSO4 + Cu	These react with the salt solution of non-metals.
They act as reducing agents (as they can easily lose electrons). Na  -> Na + + e-	These act as oxidising agents (as they can gain electrons). Cl2 + 2e- --> 2Cl-

The solution he had used was Aqua regia. Aqua regia is Latin word which means ‘Royal Water’. It is the mixture of concentrated Hydrochloric acid and concentrated nitric acid in the ratio of 3:1. It is capable of dissolving metals like Gold and Platinum. Since the outer layer of the gold bangles is dissolved in aqua regia so their weight was reduced drastically.

Copper does not react with cold water, hot water, or steam. However, iron reacts with steam. If the hot water tanks are made of steel (an alloy of iron), then iron would react vigorously with the steam formed from hot water.

3Fe + 4H₂O → Fe₃O₄ + H₂O
That is why copper is used to make hot water tanks, and not steel.

1. Which of the following property is generally not shown by metals?
(a) Electrical conduction
(b) Sonorous in nature
(c) Dullness
(d) Ductility
Ans. (c) Dullness

2. The ability of metals to be drawn into thin wire is known as
(a) ductility
(b) malleability
(c) sonorousity
(d) conductivity
Ans. (a) Ductility

3. Aluminium is used for making cooking utensils. Which of the following properties of aluminium are responsible for the same?
(i) Good thermal conductivity
(ii) Good electrical conductivity
(iii) Ductility
(iv) High melting point
(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii) and (iii)
 (d) (i) and (iv)
Ans. (d) (i) and (iv)
Explanation: Electrical conductivity and ductility have no relevance for a cooking utensil.

4. Which one of the following metals do not react with cold as well as hot water?
(a) Na
(b) Ca
(c) Mg
(d) Fe
Ans. (d) Iron (Fe)
Explanation: Sodium and calcium react vigorously with water. magnesium reacts with hot water to form magnesium oxide. Iron reacts with steam.

5. Which of the following oxide(s) of iron would be obtained on prolonged reaction of iron with steam?
(a) FeO
(b) Fe₂O₃
(c) Fe₃O4
(d) Fe₂O₃ and Fe₃O4
Ans. (c) Fe₃O4

Explanation: Following equation shows the reaction between iron and steam: 

3Fe+ 4H2O → Fe₃O₄ + 4H₂O

6. What happens when calcium is treated with water?
(i) It does not react with water
(ii) It reacts violently with water
(iii) It reacts less violently with water
(iv) Bubbles of hydrogen gas formed stick to the surface of calcium
(a) (i) and (iv)
(b) (ii) and (iii)
(c) (i) and (ii)
(d) (iii) and (iv)
Ans. (d) (iii) and (iv)
Explanation: Calcium reacts less violently with water. it starts floating because it sticks to hydrogen bubbles
Ca + H₂O -> Ca(OH)₂ + H₂

7. Generally metals react with acids to give salt and hydrogen gas. Which of the following acids does not give hydrogen gas on reacting with metals (except Mn and Mg)?
(a) H₂SO₄
(b) HCl
(c) HNO₃
(d) All of these
Ans. (c) HNO₃
Explanation: Nitric acid is a potent oxidizing agent. It reacts with hydrogen to form water. 

8. The composition of aqua-regia is
(a) Dil. HCl: Conc. HNO₃  (3:1)
(b) Conc. HCl: Dil.HNO₃  (3:1)
(c) Conc. HCl: Conc.HNO₃  (3:1)
(d) Dil. HCl: Dil. HNO₃  (3:1)

Ans. (b) Conc. HCl: Dil. HNO3 (3:1)4

9. Which of the following are not ionic compounds?
(i) KCl
(ii) HCl
(iii) CCl₄
(iv) NaCl
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (i) and (iii)
Ans. (b) (ii) and (iii)
Explanation: These are covalent compounds. Both the constituents in each compound are non-metals. 

10. Which one of the following properties is not generally exhibited by ionic compounds?
(a) Solubility in water
(b) Electrical conductivity in solid state
(c) High melting and boiling points
(d) Electrical conductivity in molten state
Ans. (b) Electrical conductivity in solid state
Explanation: Free ions are required for electrical conductivity. In ionic compounds, free ions are not available in solid state. 

11. Which of the following metals exist in their native state in nature?
(i) Cu
(ii) Au
(iii) Zn
(iv) Ag
(a) (i) and (ii) (b) (ii) and (iii)
(c) (ii) and (iv) (d) (iii) and (iv)
Ans. (c) (ii) and (iv)
Explanation: Gold and silver are noble metals and are the least reactive metals. Hence, they are found in their native state in nature

12. Metals are refined by using different methods. Which of the following metals are refined by electrolytic refining?
(i) Au
(ii) Cu
(iii) Na
(iv) K
(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii) and (iii)
(d) (iii) and (iv)
Ans. (d) (iii) and (iv)
Explanation: These metals are at the top of reactivity series. Hence, these are refined by electrolytic refining. 

13. Silver articles become black on prolonged exposure to air. This is due to the formation of
(a) Ag₃N
(b) Ag₂O
(c) Ag₂S
(d) Ag₂S  and Ag₃N₂
Ans. (c) Ag₂S

14. Galvanisation is a method of protecting iron from rusting by coating with a thin
layer of
(a) Gallium
(b) Aluminium
(c) Zinc
(d) Silver
Ans. (c) Zinc
Explanation: Applying a layer of zinc through electrolysis is called galvanization.

15. Stainless steel is very useful material for our life. In stainless steel, iron is mixed with
(a) Ni and Cr
(b) Cu and Cr
(c) Ni and Cu
(d) Cu and Au
Ans. (a) Ni and Cr

16. If copper is kept open in air, it slowly loses its shining brown surface and gains a green coating. It is due to the formation of 

(a) CuSO₄
(b) CuCO₃
(c) Cu(NO₃)₂ 
(d) CuO
Ans. (d) CuO
Explanation: When kept in open air, Copper reacts with oxygen to form copper oxide which appears as greenish layer. 

17. Generally, metals are solid in nature. Which one of the following metals is found in liquid state at room temperature?
(a) Na
(b) Fe
(c) Cr
(d) Hg 

Ans. (d) Hg
Explanation: Mercury is the metal which is present in liquid state at room temperature.

18. Which of the following metals are obtained by electrolysis of their chlorides in molten state?
(i) Na
(ii) Ca
(iii) Fe
(iv) Cu
(a) (i) and (iv)
(b) (iii) and (iv)
(c) (i) and (iii)
(d) (i) and (ii)
Ans. (d) (i) and (ii)
Explanation: These metals are at the top of reactivity series.
19. Generally, non-metals are not lustrous. Which of the following non-metal is
lustrous?
(a) Sulphur
(b) Oxygen
(c) Nitrogen
(d) Iodine
Ans. (d) Iodine

20. Which one of the following four metals would be displaced from the solution of its salts by other three metals?
(a) Mg
(b) Ag
(c) Zn
(d) Cu
Ans. (b) Ag
Explanation: Silver is the least reactive metal among the given metals.

21. 2 mL each of concentrated HCl, HNO₃ and a mixture of concentrated HCl and concentrated HNO₃ in the ratio of 3: 1 were taken in test tubes labelled as A, B and C. A small piece of metal was put in each test tube. No change occurred in test tubes A and B but the metal got dissolved in test tube C respectively. The metal could be
(a) Al
(b) Au
(c) Cu
(d) Pt
Ans. (b) Au
Explanation: Mixture in test tube C is called Aqua Regia. It dissolves gold.

22. An alloy is 
(a) an element
(b) a compound
(c) a homogeneous mixture
(d) a heterogeneous mixture
Ans. (c) A homogeneous mixture
Explanation: Components of alloy retain their chemical properties; hence alloy cannot be a compound. Composition of alloy is uniform; hence it is a homogeneous mixture. 
 

23. An electrolytic cell consists of
(i) positively charged cathode
(ii) negatively charged anode
(iii) positively charged anode
(iv) negatively charged cathode
(a) (i) and (ii)
(b) (iii) and (iv)
(c) (i) and (iii)
(d) (ii) ad (iv)
Ans. (b) (iii) and (iv)
Explanation: Negative charged particles (anions) move towards anode; which shows anode is positively charged.

24. During electrolytic refining of zinc, it gets
(a) deposited on cathode
(b) deposited on anode
(c) deposited on cathode as well as anode
(d) remains in the solution
Ans. (a) Deposited at cathode
Explanation: Zinc is positively charged and hence is deposited at negatively charged cathode.

25. An element A is soft and can be cut with a knife. This is very reactive to air and cannot be kept open in air. It reacts vigorously with water. Identify the element from the following
(a) Mg
(b) Na
(c) P
(d) Ca
Ans. (b) Na
Explanation: Sodium is soft and can be cut with knife. It reacts so vigorously with water and air that it is kept in kerosene to prevent reaction.

26. Alloys are homogeneous mixtures of a metal with a metal or non-metal. Which among the following alloys contain non-metal as one of its constituents?
(a) Brass
(b) Bronze
(c) Amalgam
(d) Steel
Ans. (d) Steel
Explanation: Steel contains carbon; along with iron.

27. Which among the following statements is incorrect for magnesium metal?
(a) It burns in oxygen with a dazzling white flame
(b) It reacts with cold water to form magnesium oxide and evolves hydrogen gas
(c) It reacts with hot water to form magnesium hydroxide and evolves hydrogen gas
(d) It reacts with steam to form magnesium hydroxide and evolves hydrogen gas
Ans. (a) It burns in oxygen with a dazzling white flame
Explanation: Magnesium does not react with cold water, so option ‘b’ is incorrect. It reacts with hot water to form magnesium oxide, so options ‘c’ and ‘d’ are incorrect.

28. Which among the following alloys contain mercury as one of its constituents?
(a) Stainless steel
(b) Alnico
(c) Solder
(d) Zinc amalgam
Ans. (d) Zinc amalgam
Explanation: Alloys of mercury are called amalgam.

29. Reaction between X and Y, forms compound Z. X loses electron and Y gains electron. Which of the following properties is not shown by Z?
(a) Has high melting point
(b) Has low melting point
(c) Conducts electricity in molten state
(d) Occurs as solid
Ans. (b) Has low melting point
Explanation: Z is an ionic compound. Ionic compound have high melting point, they occur as solid and conduct electricity in molten state

30. The electronic configurations of three elements X, Y and Z are X — 2, 8; Y — 2, 8, 7 and Z — 2, 8, 2. Which of the following is correct?
(a) X is a metal
(b) Y is a metal
(c) Z is a non-metal
(d) Y is a non-metal and Z is a metal
Ans. (d) Y is a non-metal and Z is a metal
Explanation: Y has 7 electrons in its outermost shell. This means Y is electronegative element and hence is a non-metal. Z has 2 electrons in its outermost shell. This means Z is electropositive element and hence is a metal.

31. Although metals form basic oxides, which of the following metals form an amphoteric oxide?
(a) Na
(b) Ca
(c) Al
(d) Cu
Ans. (c) Al
Explanation: Oxide of aluminium shows both acidic and basic behaviour and hence is an amphoteric oxide.

32. Generally, non-metals are not conductors of electricity. Which of the following is a good conductor of electricity?
(a) Diamond
(b) Graphite
(c) Sulphur
(d) Fullerene
Ans. (b) Graphite

33. Electrical wires have a coating of an insulting material. The material, generally used is
(a) Sulphur
(b) Graphite
(c) PVC
(d) All can be used
Ans. (c) PVC
Explanation: Sulphur is highly brittle and hence cannot be used. Graphite is good conductor of electricity and hence it cannot be used for insulation.

34. Which of the following non-metals is a liquid?
(a) Carbon
(b) Bromine
(c) Phosphorus
(d) Sulphur
Ans. (b) Bromine

35. Which of the following can undergo a chemical reaction?
(a) MgSO₄ + Fe
(b) ZnSO₄ + Fe
(c) MgSO₄ + Pb
(d) CuSO₄ + Fe
Ans. (d) CuSO₄ + Fe
Explanation: Iron is more reactive than copper. Hence, iron displaces copper from copper sulphate solution.

36. Which one of the following figures correctly describes the process of electrolytic refining?



Ans. (b)
Explanation: Copper ions are liberated from positively charged anode and getting deposited on negatively charged cathode.

Burning matchstick should be brought near the evolved gas. If matchstick burns with a pop sound, it indicates evolution of hydrogen gas.

Reaction with NaOH:

M + NaOH → Na₂MO₂ + H₂

Reaction with HCl:

 M + HCl →MCl + H₂

(a) Which material will be used as anode and cathode for refining of silver metal by this process?
 Ans. During electrolytic refining, impure metal is used as anode and pure metal is used as cathode. So, impure silver will be used as anode and pure silver will be used as cathode.
 
 (b) Suggest a suitable electrolyte also.
 Ans. Silver sulphate solution can be a suitable electrolyte.
 
 (c) In this electrolytic cell, where do we get pure silver after passing electric current?
 Ans. Pure silver will be obtained on cathode; because metals are electropositive. 

It is easier to obtain a metal from its oxide than from its sulphides or carbonates. Hence, in the process of extraction of metal from metal sulphides and carbonates, they are first converted to metal oxides.

Nitric acid is a potent oxidizing agent. It reacts with hydrogen to form water. Due to this, when a metal is treated with nitric acid, hydrogen gas is not liberated.

Compound X is iron oxide Fe₂O₃ . This reaction is called thermite reaction. This reaction is given by following equation:

2 Al  + Fe₂O₃ → 2Fe  +Al₂O₃  + heat

X is sodium because molar mass of NaOH is 40; which can be shown as follows:

Na (23) + O(16) + H (1) = 40

So, Y is NaOH

Z is hydrogen gas which easily catches fire.

Reaction between sodium and water can be given as follows:

2Na + 2H₂O → 2 NaOH + H₂

X is carbon. Diamond and graphite are allotropes of carbon. Diamond is the hardest natural substance and hence Y is diamond. Graphite is a good conductor of electricity and hence Z is graphite.

The following reaction takes place when aluminium powder is heated with MnO₂

3MnO₂(s) + 4Al(s) → 3Mn(l) +2Al₂O₃  + Heat

(a) Is aluminium getting reduced?

(b) Is  MnO₂ getting oxidised?

Ans. In this reaction, aluminium is getting oxidized because oxygen gets combined to it. Since oxygen is removed from manganese dioxide hence MnO₂ is getting reduced.

Lead and tin are the constituents of solder alloy. Solder alloy has a low melting point; which makes it suitable for welding electrical wires.

Metal A is aluminium and B is Al₂O₃ .

Reaction of aluminium oxide with HCl:

Al₂O₃ + HCl → 2AlCl₃ + 3H₂O

Reaction of aluminium oxide with NaOH: 

Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O

This metal is mercury because mercury exists as liquid at room temperature. Mercury ore is called cinnabar (HgS). When cinnabar is heated in presence of air, following reaction takes place: 

2HgS + O₂ → 2 HgO + 2 SO₂

Mercury oxide is further heated to obtain mercury:

2HgO → 2Hg + O₂

(a) Mg and N₂
Ans. Magnesium nitride (Mg₃N₂)
(b) Li and O₂
Ans. Lithium oxide (Li₂O)
(c) Al and Cl₂
Ans. Aluminum chloride (AlCl₃)
(d) K and O₂
Ans. Potassium oxide (K₂O) 

(a) ZnCO₃ is heated in the absence of oxygen?
Ans. When zinc carbonate is heated in the absence of oxygen, we get zinc oxide and carbon dioxide.

ZnCO₃ → ZnO + CO₂  

(b) a mixture of Cu₂O and Cu₂S is heated?
Ans. When a mixture of copper oxide and copper sulphide is heated, we get pure copper.
2Cu₂O + Cu₂S → 6Cu + SO₂

(a) Identify A, B and C

Ans. A is carbon, B is carbon monoxide and C is carbon dioxide.

(b) To which Group of Periodic Table does A belong?

Ans. Carbon belongs to group 14.

Iron and copper are good conductors of heat and electricity. Lead and mercury are poor conductors of heat and electricity.

Mercury (metal) and bromine (non-metal) exist in liquid state at room temperature. Caesium and gallium are metals with melting point less than 310 k.

A is calcium. It reacts with water to give calcium hydroxide. B is calcium hydroxide and is used for white washing. C is calcium oxide. The reactions are as follows:

Ca  + 2H₂O → Ca(OH)₂ +  H₂ 
Ca(OH)₂ → CaO + H₂O 
CaO + H₂O → Ca(OH)₂

A is sodium because molar mass of NaOH is 40; which can be shown as follows:
 Na (23) +O (16) +H(1)=40
 So, B is NaOH
 When sodium hydroxide is treated with aluminium oxide, we get sodium aluminate. So, C is sodium aluminate. Following reaction happens in this case: 
Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O

(a) roasting of zinc ore

2ZnS + 3O₂ → 2ZnO + 2SO₂

(b) calcination of zinc ore

ZnCO₃ → ZnO + CO₂

Copper does not react with acids. But copper gives black coloured copper oxide when it reacts with oxygen. Hence, M is copper and black coloured product is copper oxide.

2Cu + O₂ → CuO

Oxides of non-metals are acidic in nature. Hence, A is a non-metal.

Iron is more reactive than copper. Due to this, iron displaced copper from copper sulphate to form iron sulphate. A portion of the iron pot got dissolved in this process and caused holes in it. Following equation is involved in this reaction: 

CuSO₄ + Fe  →FeSO₄ + Cu

(a) Identify A, B, C and D

Ans. A is nitrogen; because nitrogen is the largest constituent of air. B is ammonia, C is nitrogen dioxide and D is nitric acid (nitric acid is a strong oxidizing agent). When nitrogen is heated with hydrogen in the presence of a catalyst, following reaction takes place:

N₂ + 3 H₂ → 2NH₃

When nitrogen is heated with oxygen, we get nitrogen dioxide.

N₂  + O₂ → 2NO₂

When nitrogen dioxide is treated with water, we get nitric acid

NO₂ + H₂O → HNO₃ 

(b) To which group of periodic table does this non-metal belong?

Ans. This non-metal belongs to Group 15.

During extraction of metals of low and medium reactivity, a respective sulphide ore is first heated in air. This helps in obtaining oxide of metal. It is easier to extract a metal from its oxide rather than from its sulphide. Hence, this step is used. Mercury is a metal of low reactivity. Mercury sulphide (cinnabar) is heated in air. Mercury sulphide gets oxidized to produce mercury oxide. 

2HgS +3O₂ → 2HgO + 2SO₂
After that, mercury oxide is reduced to obtain mercury. 
2HgO → 2Hg + O₂

Zinc is a metal of medium reactivity. It is found as zinc blende (ZnS).
 Zinc blende is roasted to obtain zinc oxide. After that, zinc oxide is reduced to obtain pure zinc. 

2ZnS + 3O₂ → ZnO + 2SO₂

After that, mercury oxide is reduced to obtain mercury.
ZnO + C → Zn + CO 

(a) Reactivity of Al decreases if it is dipped in HNO₃.
Ans. Nitric acid is a strong oxidizing agent. Due to this, when aluminium is dipped in nitric acid, a layer of aluminium oxide is deposited on aluminium. As a result; reactivity of aluminium decreases when it is dipped in nitric acid. 

(b) Carbon cannot reduce the oxides of Na or Mg
 Ans. Sodium and magnesium are highly reactive metals. Hence, they have higher affinity to oxygen than to carbon. Due to this, carbon fails to reduce the oxides of sodium or magnesium.
 
(c) NaCl is not a conductor of electricity in solid state whereas it does conduct electricity in aqueous solution as well as in molten state
 Ans. NaCl is an ionic compound. Ionic compounds do not conduct electricity in solid state. But ionic compounds are good conductors of electricity in molten state and in aqueous solution.
 
(d) Iron articles are galvanised.
Ans. Iron has a tendency to react with atmospheric moisture. This process is called rusting and leads to corrosion of iron. Iron articles are galvanized to prevent rusting of iron.

(e) Metals like Na, K, Ca and Mg are never found in their free state in nature.
 Ans. Na, K, Ca and Mg are highly reactive metals. They can easily form compound with most of the elements. Due to this, these metals are not found in their free state in nature. 
 

(a) Roasting of copper (1) sulphide
Ans. 2Cu₂S + 3O₂ → 2Cu₂O + 2SO₂

(b) Reduction of copper (1) oxide with copper (1) sulphide.
2Cu₂O + Cu₂S → 6Cu + SO₂

(c) Electrolytic refining
Ans. At cathode: Cu²⁺ + 2e^- → Cu

(ii) Draw a neat and well labelled diagram for electrolytic refining of copper


Fig. 3.2 Electrolytic refining of copper. The electrolyte is a solution of acidified copper sulphate. The anode is impure copper, whereas, the cathode is a strip of pure copper. On passing electric current, pure copper is deposited on the cathode.

X is sodium, Y is magnesium and Z is iron. 

X is sodium, Y is magnesium and Z is iron.
2Na + H₂O →  2NaOH + H₂
Mg + H₂O →  Mg(OH)2 + H₂
3Fe + H₂O → Fe₃O₄  +4 H₂
Their sequence in reactivity series is as follows: 
 Fe < Mg < Na.

A is sodium. B is chlorine (atomic number 17). C is sodium chloride and D is sodium hydroxide.

2 Na  + Cl₂  → NaCl 

Electrolysis of sodium chloride can be given by following equation:

2NaCl +2 H₂O → 2NaOH + Cl₂ + H₂

When a carbonate ore is heated, we get carbon dioxide. A carbonate ore is calcinated to obtain oxide of the metal. Following equation shows calcinations of zinc carbonate.

ZnCO₃ +  ZnO  → CO₂

When a sulphide ore is roasted, we get Sulphur dioxide. Zinc sulphide is roasted to obtain zinc oxide.

2ZnS + 3O₂ → 2ZnO + 2SO₂

After any of the above steps; zinc oxide is reduced to obtain pure zinc.

ZnO + C → Zn +  CO