Which hydroxide will have the lowest value of solubility product at normal temperature $({25\,^oC})$?

Assign $A, B, C, D$ from the given type of reaction.
$FeS \downarrow + 2HCl \longrightarrow FeCl_2 + H_2S \uparrow$

$K_{sp}$ 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 of $CaCl_2$ is $1.11 \times 10^{-8} \ g/100 \ mL$. If the molar mass of $CaCl_2$ is $111 \ g/mol$,find the $K_{sp}$.

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 a sparingly soluble salt $AX_2$ is $1 \times 10^{-4} \ mol \ dm^{-3}$ at $298 \ K$. Calculate its solubility product $(K_{sp})$?