The solubility products of NiS, ZnS, CdS, and HgS are \(4.7\times10^{-5}\), \(1.6\times10^{-24}\), \(8\times10^{-27}\), and \(4\times10^{-53}\) respectively. An aqueous solution contains Ni\(^{2+}\), Zn\(^{2+}\), Cd\(^{2+}\), and Hg\(^{2+}\) of equal concentration. H\(_2\)S gas is passed into this solution very slowly. The first and the last ions that precipitate as sulphides are respectively: