(i) The nature of the solution is acidic. It is a mixture of conc. HNO₃, and conc. HCI in the ratio of 1 : 3. It can dissolve gold as it is an oxidising agent.
(ii) Pure gold is 24 carat gold which is very soft.

Metals high up in reactivity series are extracted by electrolytic reduction. While those in the middle are extracted first by converting into oxide and then reducing by carbon.
Same method cannot be used because metals have more affinity for oxygen than carbon.
Molten sodium chloride is taken for electrolytic reduction. The metals are deposited at the cathode and chlorine is liberated at anode.
At cathode: Na⁺ + e^- \(\longrightarrow \)Na
At anode: 2Cl^- \(\longrightarrow \) C1₂ + 2e^-

(a) The main ore of aluminium is bauxite ore. Its formula is A1₂0₃.The impurities sociated with this ore are iron oxide and sand. .
(b) The reaction involved in obtaining pure alumina from mineral bauxite having impurities of iron oxide and silica are:
     (i) \(\underset { Aluminiumoxide\\ (frombauxiteore) }{ { A1 }_{ 2 }{ O }_{ 3 } } +\underset { Sodiumhydroxide\\ \quad (hot) }{ 2NaOH(aq) } \rightarrow \underset { Sodiumaluminate\\ \quad (Soluble) }{ { 2NaA1O }_{ 2 }(aq) } +\underset { Water }{ { H }_{ 2 }O(1) } \)
    The iron oxide and silica (sand) present in the bauxite ore do not dissolve in sodium hydroxide solution. Therefore, they are separated by filtration.
     (ii) \(\underset { Sodiumaluminate }{ { NaA1O }_{ 2 }(aq) } +\underset { Water }{ { 2H }_{ 2 }O(1) } \rightarrow \underset { Aluminiumhydroxide\\ \quad (Whiteppt) }{ { A1(OH) }_{ 3 }(s) } +\underset { Sodiumhydroxide }{ NaOH(aq) } \)
     (iii) \(\underset { Aluminiumhydroxide }{ { 2A1(OH) }_{ 3 }(s) } \underrightarrow { heat } \underset { Aluminiumoxide\\ \quad (Pure) }{ { A1 }_{ 2 }{ O }_{ 3 }(s) } +\underset { Steam }{ { 3H }_{ 2 }O(g) } \)

(a) The arrangement of metals in a vertical column in the order of decreasing reactivity is called the 'activity series' of metals. 
Following is the order of decreasing order of reactivity:
Cu> Fe> Zn> AI> Mg
(b) (i) When some zinc is put into blue copper sulphate solution, the blue colour of the copper sulphate solution fades gradually due to the formation of colourless zinc sulphate and red-brown copper metal is deposited on the zinc strip.
                           \(\underset { Coppersulphate\\ \quad (blue) }{ { CuSO }_{ 4 }(aq) } +\underset { Zinc }{ Zn } \rightarrow \underset { Zincsulphate\\ (Colourless) }{ { ZnSO }_{ 4 }(aq) } +\underset { \quad Copper\\ (Red-brown) }{ Cu(s) } \)
(ii) No reaction will take place since copper is less reactive than iron and hence will not displace it from ferrous sulphate solution.
(c) Sodium metal combines with hydrogen gas to form sodium hydride.
                           \(\underset { Sodiummetal }{ 2Na(s) } +\underset { Hydrogengas }{ { H }_{ 2 }(g) } \rightarrow \underset { Sodiumhydride }{ 2NaH(s) } \)

(a) The eating up of metals by the action of air and moisture on their surface is called corrosion.
      (i) Metal which does not corrode on being kept in the atmosphere is gold.
     (ii) Metal which corrodes on being kept in the atmosphere is iron.
(b) Take three boiling tubes and label them as A, B, and C. Place clean iron nails, free from rust, in each tube. Add water to tube A in such a manner that some parts of the nails are exposed to air and seal it with the help of a rubber cork. Add boiled water to tube B in such a way that the nails are completely submerged. Then, pour some amount of kerosene oil in the tube and seal it with the help of a rubber cork. Add anhydrous calcium chloride to tube C and then seal it. Leave the tubes undisturbed for two weeks and observe the changes. 

(a) The reaction involved in obtaining pure alumina from the mineral bauxite having impurities of iron oxide and silica is:
        (i) \(\underset { Aluminiumoxide\\ (frombauxiteore) }{ { AI }_{ 2 }{ O }_{ 3 }(s) } +\underset { Sodiumhydroxide\\ \quad (hot) }{ 2NaOH(aq) } \rightarrow \underset { Sodiumaluminate\\ \quad (Soluble) }{ { 2NaAIO }_{ 2 }(aq) } +\underset { Water }{ { H }_{ 2 }O(I) } \)
    The iron oxide and silica (sand) present in the bauxite ore do not dissolve in sodium hydroxide solution. Therefore, they are separated by filtration.
       (ii) \(\underset { Sodiumaluminate }{ { NaAIO }_{ 2 }(aq) } +\underset { Water }{ { 2H }_{ 2 }O(I) } \rightarrow \underset { Aluminiumhydroxide\\ \quad (Whiteppt) }{ { AI(OH) }_{ 3 }(s) } +\underset { Sodiumhydroxide }{ NaOH(aq) } \) 
       (iii) \(\underset { Aluminiumhydroxide }{ { 2AI(OH) }_{ 3 }(s) } \underrightarrow { heat } \underset { Aluminiumoxide\\ \quad (Pure) }{ { AI }_{ 2 }{ O }_{ 3 }(s) } +\underset { Steam }{ { 3H }_{ 2 }O(g) } \)
(b)

(i) Concentrated sulphuric acid is called the king of chemicals as it is a very strong acid and is highly corrosive.
(ii) (a) When concentrated sulphuric acid acts on sulphur, sulphur dioxide gas is evolved.
        \(\underset { Suphur }{ S(s) } +\underset { Suphuricacid(conc.) }{ { 2H }_{ 2 }{ SO }_{ 4 }(I) } \underrightarrow { \Delta } \underset { Sulphurdioxide }{ { 3SO }_{ 2 }(g) } +\underset { Water }{ { 2H }_{ 2 }O(I) } \)
    (b) When dilute sulphuric acid acts on sodium carbonate, carbon dioxide gas is evolved.
         \(\underset { Sodiumcarbonate }{ { Na }_{ 2 }{ CO }_{ 3 }(g) } +\underset { Sulphuricacid }{ { H }_{ 2 }{ SO }_{ 4 }(aq) } \rightarrow \underset { Sodiumsulphate }{ { Na }_{ 2 }{ SO }_{ 4 }(aq) } +\underset { Carbondioxide }{ { CO }_{ 2 }(g) } +\underset { Water }{ { H }_{ 2 }O(I) } \)
(iii) (a) When concentrated sulphuric acid is added to blue copper sulphate crystals, white coloured anhydrous copper sulphate is formed.
        \(\underset { Copper(II)sulphatepentahydrate\\ \quad \quad (BlueCrystal) }{ { CuSO }_{ 4 }.{ 5H }_{ 2 }O } \overset { { conc.H }_{ 2 }{ SO }_{ 4 } }{ \underset { { -5H }_{ 2 }O }{ \longrightarrow } } \underset { Anhydrouscopper(II)sulphate\\ \quad \quad (Whitepowder) }{ { CuSO }_{ 4 } } \)
     (b) When concentrated sulphuric acid is added to colourless cane sugar crystals, it dehydrates sugar to a black mass of carbon known as sugar charcoal.
            \(\underset { Sugar\\ (White) }{ { C }_{ 12 }{ H }_{ 22 }{ O }_{ 11 } } \overset { { conc.H }_{ 2 }{ SO }_{ 4 } }{ \underset { { -11H }_{ 2 }O }{ \longrightarrow } } \underset { Carbon\\ (Black) }{ 12C } \)

(i) An alloy is a homogenous mixture of two or more metals. It sometimes contains a non -metal component also.
(ii) It is made by heating the components in a definite proportion and then uniformly mixing them in the molten state and then cooling.
(iii) Two purposes of making alloys are:
     (a) To make a substance resistant to corrosion
     (b) To make a substance strong and hard
(iv) Constituents of Stainless steel:
     Iron, nickel, and chromium
(v) Two properties of stainless steel are:
     (a) It is resistant to corrosion.
     (b) It is more durable.
(vi) Constituents of Brass:
      Copper and Zinc
(vii) Two properties of brass are:
       (a) It is resistant to corrosion.
      (b) It is more malleable.

Ore A gives CO₂ and ore B gives SO₂ . Therefore, ores are MCO₃ and MS.
A can be converted into metal by the following steps :
\({ MCO }_{ 3 }\underrightarrow { Calcination } MO+{ CO }_{ 2 }\\ MO+C\underrightarrow { Reduction } M+CO\)
B can be converted into metal by the following steps :
\(2MS+{ 3O }_{ 2 }\underrightarrow { Roasting } 2MO+{ 2SO }_{ 2 }\\ \quad \quad \quad MO+C\rightarrow M+CO\)