The values of ${\mathrm{K}}_{\mathrm{sp}}$ for CuS, ${\mathrm{Ag}}_2\mathrm{S}$ and HgS are ${10}^{-31}, {10}^{-42} \mathrm{and} {10}^{-54}$ respectively. The correct order of their solubility in water is

${\mathrm{Ag}}_2\mathrm{S}$ > CuS > HgS

Solubility of CuS = $\sqrt{{10}^{-31}} = 3.16 \times {10}^{-16} mol/L$

Solubility of  ${\mathrm{Ag}}_2\mathrm{S}$

$= \sqrt[3]{\frac{K_{sp}}{4}} = \sqrt[3]{\frac{{10}^{-42}}{4}} = 6.3 \times {10}^{-5} mol/L$

Solubility of HgS = $\sqrt{K_{sp}} = \sqrt{{10}^{-54}}$

$= {10}^{-27} mol/L$