Which of the following reduction reactions are actually employed in the commercial extraction of metals?

F e_{2} O_{3} + 2 A l \to A l_{2} O_{3} + 2 F e

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C r_{2} O_{3} + 2 A l \to A l_{2} O_{3} + 2 C r

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2 N a [A u (C N)_{2}] + Z n \to N a_{2} [Z n (C N)_{4}] + 2 A u

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C u_{2} O + H_{2} \to 2 C u + H_{2} O

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Solution

The correct option is C $2 N a [A u (C N)_{2}] + Z n \to N a_{2} [Z n (C N)_{4}] + 2 A u$
(a) Iron is commercially extracted by reduction with $C$ and $C O$ . Thus (a) is incorrect.

(b) Chromium is extracted commercially by reduction with aluminium.

(c) Leaching of $A u_{2} S$ is carried out by heating it with a dilute solution of $N a C N$ in the presence of $O_{2}$ .
$A u_{2} S + 4 N a C N ⟶ 2 N a [A u (C N)_{2}] + N a_{2} S$

Treatment of the cyanide compound with zinc takes place via displacement reaction.
$2 N a [A u (C N)_{2}] + Z n \to N a_{2} [Z n (C N)_{4}] + 2 A u$

(d) The commercial metallurgical process for the extraction of metallic copper from its sulphide ore involves the oxidation of $C u_{2} S$ to $C u_{2} O$ and the auto-reduction of a mixture of $C u_{2} S$ and $C u_{2} O$ to copper metal.
Thus, (d) is incorrect.

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