Copper sulphate dissolved in excess of KCN to give:-

Options

A. `[Cu(CN)_(4)]^(2-)`
B. `Cu(CN)_(2)`
C. `CuCN`
D. `[Cu(CN)_(4)]^(3-)`

Answer

D

Explanation

KCN first reduces cupric ions to cuprous ions which are precipitated as cuprous cyanide. This reacts with excess of `CN^(-)` to form soluble four-coordinated complex `[Cu(CN)_(4)]^(3-)` which is tetrahedral in shape.
`2Cu^(2+)+4CN^(-)rarr2Cu^(+)CN^(-)+underset("Cyanogen")((CN)_(2))`
`CuCN+3CN^(-)rarr[Cu(CN)_(4)]^(3-)`
or `3KCN+CuCNrarrK_(3)[Cu(CN)_(4)]`