$\mathrm{PbS}\left(\mathrm{s}\right)\stackrel{}{\rightleftharpoons }{\mathrm{Pb}}^{2+}\left(\mathrm{aq}\right)+{\mathrm{S}}^{2-}\left(\mathrm{aq}\right)$

Let us consider the solubility of $\mathrm{PbS}$ is "$\mathrm{S}$" $\mathrm{M}$.

Thus,

Solubility product $=\left[{\mathrm{Pb}}^{2+}\left(\mathrm{aq}\right)\right]\left[{\mathrm{S}}^{2-}\left(\mathrm{aq}\right)\right]$

$\mathrm{Ksp}=\left[{\mathrm{Pb}}^{2+}\left(\mathrm{aq}\right)\right]\left[{\mathrm{S}}^{2-}\left(\mathrm{aq}\right)\right] \cdots \left(\mathrm{i}\right)$

We know

${\mathrm{K}}_{\mathrm{sp}}={\mathrm{S}}^2$

$\mathrm{S}=\sqrt{{\mathrm{K}}_{\mathrm{sp}}}=\sqrt{8\times {10}^{-28}}=2\sqrt{2}\times {10}^{-14}$

$=2.82\times {10}^{-14}$

$=282\times {10}^{-16}$