A solution of a metal ion when treated with KI gives a red precipitate which dissolves in excess KI to give a colourless solution. Moreover, 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

A

$$Pb^{2+}$$

B

$$Hg^{2+}$$

C

$$Cu^{2+}$$

D

$$Co^{2+}$$