Which of the following is most soluble?

The following is most soluble is $\mathrm{MnS}\left(K_{\mathrm{sp}}^{\circ }=7\times {10}^{-16}\right)$.

An electrolyte becomes more soluble as the ionic product, or solubility product, rises. Now, 

${\mathrm{K}}_{\mathrm{sp}}\left(\mathrm{MnS}\right)>{\mathrm{K}}_{\mathrm{sp}}\left(\mathrm{CuS}\right)>{\mathrm{K}}_{\mathrm{sp}}\left({\mathrm{Ag}}_2\mathrm{S}\right)>{\mathrm{K}}_{\mathrm{sp}}\left({\mathrm{Bi}}_2{\mathrm{S}}_3\right)$

MnS will be the most soluble as a result.

Hence the option D is correct.