A solution of a metal ion when treated with KI gives a red precipitate which dissolves in excess KI to give a colourless solution. Morever, the solution of metal ion on treatment with a solution of cobalt (II) thiocyanate gives rise to a deep blue crystalline precipitate. The metal ion is :

Options

A. `Pb^(2+) `
B. `Hg^(2+) `
C. `Cu^(2+)`
D. `Co^(2+)`

Answer

B

Explanation

`Hg^(2+) (aq) + 2KI (aq) to underset("(Scarlet red)")(HgI_2 (s)) + 2K^(+) (aq)`
`HgI_2(s) + 2KI (aq) to K_2[HgI_4](aq)`
`Co^(2+)(aq) + Hg^(2+) (aq) + 4SCN^(-) (aq) to underset("Deep blue ")(Co[Hg(SCN)_4])(s)`