$ `Cu^(2+)` and `Cd^(2+)` are separated by first adding KCN solution and then passing `H_(2)S` gas.
! KCN reduces `Cu^(2+)` to `Cu^(+)` and forms a complex with it.

Options

A. Both A and R are true and R is the correct explanation of A
B. Both A and R are true but R is not a correct explanation of A
C. A is true but R is false
D. A is false but R is true.

Explanation

Correct explanation : KCN forms complex with `Cu^(+)` and `Cd^(2+)` as `K_(3)[Cu(CN)_(4)]` and `K_(2)[Cd(CN)_(4)]` respectively. On passing `H_(2)S` only `Cd^(2+)` complex gets decomposed to yellow CdS ppt.