Which of the following sulphides has the lowest solubility product?

Which compound does not dissolve in hot dilute $HNO_3$?

If the concentration of sodium ions in a saturated solution of $Na_2SO_4$ is $10^{-5} \ mol/L$,find the solubility product $(K_{sp})$.

The concentration of a saturated solution of $Mg(OH)_2$ is $8.2 \times 10^{-4} \ g \ L^{-1}$ at $298 \ K$. Calculate its solubility product $(K_{sp})$. (Molar mass of $Mg(OH)_2 = 58 \ g \ mol^{-1}$)

What is the value of $K_{sp}$ for a saturated solution of $Ba(OH)_2$ having $pH = 12$?

For $AgCl$,$K_{sp} = 1.2 \times 10^{-10}$ and for $AgBr$,$K_{sp} = 3.5 \times 10^{-13}$. What is the relationship between their solubilities $(S)$?