$A$ 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 the 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
  $Co^{2+}$