In the separation of `Cu^(2+)` and `Cd^(2+)` of Iind group in qualitative analysis of cations, tetraamminecopper (II) sulphate and tetramminecadmium (II) sulphate react with KCN to form the corresponding cyano complex. Which one of the following pairs of the complexes and their relative stability enables the separation of `Cu^(2+)` and `Cd^(2+)` ?

Options

A. `K_(3)[Cu(CN)_(4)] :` more stable and
`K_(2)[Cd(CN)_(4)] :` less stable
B. `K_(2)[Cu(CN)_(4)]` : less stable
and `K_(2)[Cd(CN)_(4)]` : more stable
C. `K_(2)[Cu(CN)_(4)]` : more stable and
`K_(2)[Cd(CN)_(4)]` : less stable
D. `K_(3)[Cu(CN)_(4)]` : less stable and
`K_(2)[Cd(CN)_(4)]` : more stable

Answer

A

Explanation

`K_3[Cu(CN)_4]` is more stable than `K_2[Cd(CN)_4]` and therfore , `Cu^(2+)` ions are not precipitated while `Cd^(2+)` ions are precipitated.