During the metallurgy of gold, from which solution gold is separated in metallic form?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → [Au(CN)2]-
Gold is extracted by the cyanide process (leaching), which uses the formation of a stable complex:
Leaching: the powdered ore is treated with dilute NaCN solution in the presence of air. Gold dissolves as the soluble complex [Au(CN)2]−.
\( \displaystyle \ce{4Au + 8CN^- + 2H2O + O2 -> 4[Au(CN)2]^- + 4OH^-} \)
Recovery: the solution is treated with zinc, a more reactive metal, which displaces gold as the metal.
\( \displaystyle \ce{2[Au(CN)2]^- + Zn -> [Zn(CN)4]^2- + 2Au} \)
In the complex, x + 2(−1) = −1, so gold is in the +1 state and is reduced to metallic gold by zinc. So gold is separated from the [Au(CN)2]− solution.
NCERT (2026-27 edition):
Importance and Applications of Coordination Compounds – …
