Extraction of gold and silver involves leaching the metal with `CN^(-)` ion. The metal is recovered by

Options

A. roasting of metal complex
B. calcination followed by roasting
C. thermal decomposition of metal complex
D. displacement of metal by some other metal from the complex ion

Answer

D

Explanation

`2M+ 4NaCb_((aq)) overset(O_(2))to 2Na[M(CN)_(2)]+2NaOH`
`2Na[M(CN)_(2)]+ Zn overset(O_(2))to Na_(2)[Zn(CN)_(4)]+2M`