Which of the following sulphides has the lowest solubility product?

The solubility product of $BaCl_2$ is $4 \times 10^{-9}$. Its solubility in $mol/L$ is .......

Calculate the minimum concentration of sulphate ion required to precipitate $BaSO_4$ in a solution containing $10^{-4} \ mol/L$ of $Ba^{2+}$. $(K_{sp} \ BaSO_4 = 4 \times 10^{-10})$

$K_{sp}$ for $Cr(OH)_3$ is $1.6 \times 10^{-30}$. What is the molar solubility of this salt in water?

Consider two Group $IV$ metal ions $X^{2+}$ and $Y^{2+}$. $A$ solution containing $0.01 \ M$ $X^{2+}$ and $0.01 \ M$ $Y^{2+}$ is saturated with $H_2S$. The pH at which the metal sulphide $YS$ will form as a precipitate is . . . . . . (Nearest integer). (Given: $K_{sp}(XS)=1 \times 10^{-22}$ at $25^{\circ} C$, $K_{sp}(YS)=4 \times 10^{-16}$ at $25^{\circ} C$, $[H_2S]=0.1 \ M$ in solution, $K_{a1} \times K_{a2}(H_2S)=1.0 \times 10^{-21}$, $\log 2=0.30, \log 3=0.48, \log 5=0.70$)

For a sparingly soluble salt $A_pB_q$,what is the relationship between its solubility $(S)$ and solubility product $(K_{sp})$?