The solubility products of $NiS$,$ZnS$,$CdS$,and $HgS$ are $4.7 \times 10^{-5}$,$1.6 \times 10^{-24}$,$8 \times 10^{-27}$,and $4 \times 10^{-53}$ respectively. An aqueous solution contains $Ni^{2+}$,$Zn^{2+}$,$Cd^{2+}$,and $Hg^{2+}$ of equal concentration. $H_2S$ gas was passed into this solution very slowly. The first and the last ions that precipitate as sulphides are respectively.

• A
  $Ni^{2+}$,$Hg^{2+}$
• B
  $Hg^{2+}$,$Cd^{2+}$
• C
  $Zn^{2+}$,$Hg^{2+}$
• D
  $Hg^{2+}$,$Ni^{2+}$