Which of the following metal sulphides has maximum solubility in water?

Question

(a) HgS $K_{sp} = 10^{-54}$
(b) CdS $K_{sp} = 10^{-30}$
(c) FeS $K_{sp} = 10^{-20}$
(d) ZnS $K_{sp} = 10^{-22}$