AIIMS2017Chemistry-Metallurgy

AIIMS 2017 Chemistry Gold Cyanidation MCQ Question

Type: MCQ-conceptual-Medium-Class 12

In the equation,

$4\text{M} + 8\text{CN}^- + 2\text{H}_2\text{O} + \text{O}_2 \rightarrow 4[\text{M}(\text{CN})_2]^- + 4\text{OH}^-$

Identify the metal (M)

$\text{Au}$

$\text{Fe}$

$\text{Zn}$

$\text{Cu}$

Correct Answer

Option A

Detailed Explanation

In the given reaction, gold (Au) is oxidized as it loses electrons to form the complex ion [Au(CN)₂]⁻, indicating that it undergoes oxidation. The oxidation state of gold increases from 0 in elemental gold to +1 in the complex ion, confirming that oxidation occurs. Options B (reduction) and C (displacement) are incorrect; reduction involves gaining electrons, which is not happening here, and displacement reactions involve one element replacing another in a compound, which does not apply to this reaction. Option D (none of these) is also incorrect as the reaction clearly demonstrates oxidation.

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