(i) Gold, one of the expensive and precious metals. It is used for coinage, and has been used as standard for monetary systems in some countries.
(ii) It is used extensively in jewellery in its alloy form with copper.
(iii) It is also used in electroplating to cover other metals with a thin layer of gold which are used in watches, artificial limb joints, cheap jewellery, dental fillings and electrical connectors.
(iv) Gold nanoparticles are also used for increasing the efficiency of solar cells and also used an catalysts.

(i) Copper is used for making coins and ornaments along with gold and other metals.
(ii) Copper and its alloys are used for making wires, water pipes and other electrical parts.

(i) Simple roasting of some of the ores give the crude metal. In such cases, the use of and hydrogen which does not rust and gives reducing agents is not necessary.
(ii) For example, mercury is obtained by Write the chemical composition of the roasting of its ore cinnabar (HgS)
\(Hg{ S }_{ (s) }+{ O }_{ 2(g) }\longrightarrow { Hg }_{ (I) }+{ SO }_{ 2 }\uparrow \)

(i) Metallic oxides such as Cr₂O₃ can be reduced by an aluminothermic process.
(ii) In this process, the metal oxide is mixed with aluminum powder and placed in a fire clay crucible.
(iii)To initiate the reduction process, an ignition mixture (usually magnesium and barium peroxide is used 
\({ BaO }_{ 2 }+Mg\longrightarrow Bao+MgO\)
(iv) During the above reaction a large amount of heat is evolved (temperature up to 2400°C, is generated and the reaction enthalpy is: 852 kJ mol^-1 which facilitates the reduction of Cr₂O₃ by aluminium power.
\({ Cr }_{ 2 }{ O }_{ 3 }+2Al\overset { \Delta }{ \longrightarrow } 2Cr+{ Al }_{ 2 }{ O }_{ 3 }\)

(i) This method can be applied to the oxides of the metals (Fe, Pb, Cu) having less electropositive character than hydrogen
\(\mathrm{Ag}_{2} \mathrm{O}_{(s)}+\mathrm{H}_{2(g)} \longrightarrow 2 \mathrm{Ag}_{(s)}+\mathrm{H}_{2} \mathrm{O}_{(l)}\)
(ii) Nickel oxide can be reduced to nickel by using a mixture of hydrogen and carbon monoxide (water gas)
(iii) \({ 2NiO }_{ (s) }+{ CO }_{ (g) }+{ H }_{ 2(g) }\longrightarrow 2{ Ni }_{ (s) }+{ CO }_{ 2(g) }+{ H }_{ 2 }{ O }_{ (l) }\)

(i) into metal using carbon as a reducing agent. In this method the oxide ore of the metal is mixed with coal (coke) and heated strongly in a furnace (usually in a blast furnace).
(ii) This process can be applied to the metals which do not form carbides with carbon at the reduction temperature
\({ ZnO }_{ (s) }+{ C }_{ (s) }\longrightarrow { Zn }_{ (s) }+{ { CO }_{ (g) }\uparrow }\)

(i) If value of \(\triangle\)G is fur any reaction then to make such reaction spontaneous it is coupled with another reaction of large negative \(\triangle\)G value, so that the sum of two \(\triangle\)G becomes negative. This is known as coupling of reaction.
(ii) In the metallurgy, thermodynamically infeasible reaction is coupled with a reaction which has more negative G, so that net \(\triangle\)G become negative.

(i) Aluminium cannot be extracted by melting process due to the following reasons.
(a) Aluminium (AI) being highly electropositive element has very: strong affinity for oxygen. So, Al₂O₃ is very stable compound and cannot be reduced by C.
(b) On heating Al₂O₃ with C, aluminium carbide is formed 
\({ 2Al }_{ 2 }{ O }_{ 3 }+9C\longrightarrow { Al }_{ 4 }{ C }_{ 3 }+6CO\)
(ii) Below 1073 k, CO is more effective, because the \(\Delta { G }^{ 0 }\) value for the conversion of CO into CO₂ is more negative.