Which of the following sulphides has the lowest solubility product?

Which of the following would increase the solubility of $Pb(OH)_2$?

$K_{sp}$ for $CaSO_4$ is $9 \times 10^{-6}$. The minimum volume of water needed to dissolve $1 \ g$ of $CaSO_4$ at $298 \ K$ temperature is ...... (in $L$)

The solubility product of silver sulphide is $3.2 \times 10^{-11}$. Its solubility at the experimental temperature is

The solubility product of $BaSO_4$ is $1 \times 10^{-10}$ at $298 \ K$. The solubility of $BaSO_4$ in $0.1 \ M \ K_2SO_4 \ (aq)$ solution is $......... \times 10^{-9} \ g \ L^{-1}$ (nearest integer). Given: Molar mass of $BaSO_4$ is $233 \ g \ mol^{-1}$.

The solubility of $BaSO_4$ in pure water (in $g \, L^{-1}$) is closest to
[Given: $K_{sp}$ for $BaSO_4$ is $1.0 \times 10^{-10}$ at $25^{\circ} C$. Molecular weight of $BaSO_4$ is $233 \, g \, mol^{-1}$]