question_answer

An aqueous solution contains \[N{{i}^{2+}},C{{o}^{2+}}\]and\[P{{b}^{2+}}\]ions    at    equal concentrations. The solubility product of \[\text{NiS, PbS}\]and \[\text{CoS}\]in water at \[\text{25}{{\,}^{\text{o}}}\text{C}\]are \[\text{1}\text{.4}\times \text{1}{{\text{0}}^{-24}},\]and\[3\times {{10}^{-26}},\]respectively. Indicate which of these ions will be precipitated first and last   when   sulphide   concentration is progressively increased from zero?

A)  NiS and PbS   

B)  NiS and CoS      

C)  CoS and NiS   

D)  PbS and NiS