Correct Answer - D
Extraction of gold and silver involves leaching with `CN^(-)` ion. Silver is later recovered by distillation of Zn.
In the metallurgy of silver or gold, the respective metal is leached with a dilute solution of NaCN or KCN in the presence of air to obtain the metal in solution as complex. From the complex, metal is obtained later by replacement.
In general.
`4M(s) + 8CN^(-)(aq)+2H_(2)O(aq)+O_(2)(g)rarr4[M(CN)_(2)]^(-)(aq)+4OH^(-)(aq)`
`2[M(CN)_(2)]^(-)(aq)+Zn(s) rarr[Zn(CN)_(4)]^(2-)(aq)+2M(s)`
M = Ag or Au
This method is known as Mac-Arthur Forest cyanide process.
