Potassium cyanide is used for separating

Options

A. `Co^(2+)` and `Ni^(2+)`
B. `Mn^(2+)` and `Zn^(2+)`
C. `Ba^(2+)` and `Ca^(2+)`
D. `Cu^(2+)` and `Cd^(2+)`

Explanation

(A) When heated with KCN solution `Ni^(2+)` forms potassium nickelocyanide `K_(2)[Ni(CN)_(4)]` and `Co^(2+)` forms potassium cobaltocyanide, `K_(2)[co(CN)_(4)]`. On treatement with NaOH and `Br_(2)` water, `K_(2)[co(CN)_(4)]` is oxidised to very stable potassium cobalticyanide `K[Co(CN)_(4)]` and does not yeild `Co^(3+)` ions while potassium nickelcyanide being unstable, decomposes to black nickelic oxide giving rise to Ni ions `2K_(2)[Ni(CN)_(4)]+4NaOH +[O] to Ni_(2)O_(3) +4NaCN +2H_(2)O +KCN `
(D) When treated with KCN, both copper and cadmium forms respectively potassium cuprocyanide `K_(3)[Cu(CN)_(4)]` and potassiun cadmium cyanide, `K_(2)[Cd(CN)_(4)]`. `K_(2)[Cd(CN)_(4)]` is unstable and produces through `Cd^(2+)` ions while `K_(3)[Cu(CN)_(4)]` is stable and does not yield `Cu^(2+)` ions.