Statement I : Leaching of gold with cyanide ion in absence of air / O₂ leads to cyano complex of Au(III).
Statement II : Zinc is oxidized during the displacement reaction carried out for gold extraction.
In the light of the above statements, choose the correct answer from the options given below.

Solution

Chemistry ma’am · 4 steps

Gold needs oxygen to dissolve in cyanide, and even then it only reaches +1, not +3.

1. Leaching needs air. Gold is a noble metal and CN⁻ alone cannot oxidise it. Dissolved O₂ is the oxidising agent, so leaching is done with air bubbled through the slurry.

   4Au + 8CN⁻ + 2H₂O + O₂ → 4[Au(CN)₂]⁻ + 4OH⁻

2. Statement I fails twice. Without air or O₂ the gold is not oxidised, so no cyano complex forms. Even with air, the complex is [Au(CN)₂]⁻, where gold is +1, not +3. Statement I is incorrect.
3. Displacement by zinc. Zinc is more reactive than gold, so it pushes gold out of the complex: 2[Au(CN)₂]⁻ + Zn → [Zn(CN)₄]²⁻ + 2Au. Zinc goes from 0 to +2, so it is oxidised. Statement II is correct.
4. So. Statement I is incorrect and Statement II is correct, which is option (d).

The idea to keep. Cyanide leaching of Au and Ag always needs O₂ as the oxidant and gives the +1 complex [M(CN)₂]⁻. Zinc then reduces it back to the metal and is itself oxidised to [Zn(CN)₄]²⁻.

Answer from the NTA final answer key. Solution by PrepWiser.