For which salt is the molar solubility, s, is approximately equal to $4\times {10}^{-6}\mathrm{M}$ ?

The salt for which the molar solubility, s, is approximately equal to $4\times {10}^{-6}\mathrm{M}$  is ${\mathrm{MnCO}}_3{K}_{sp}=2\times {10}^{-11}$,

As,

$$\begin{gathered} s=\sqrt{2\times {10}^{-11}} \\ \mathrm{s}=4.5\times {10}^{-6} \mathrm{M} \end{gathered}$$