The salt having the least solubility in water is

Match the following metal sulfides with their respective solubility product $(K_{sp})$ values:

Metal sulfide	Solubility product
$A$. $PbS$	$I$. $4.0 \times 10^{-53}$
$B$. $HgS$	$II$. $8.0 \times 10^{-28}$
$C$. $MnS$	$III$. $1.6 \times 10^{-24}$
$D$. $ZnS$	$IV$. $2.5 \times 10^{-13}$

The moles of $Ag^{+}$ which must be added to decrease the concentration of $Cl^{-}$ from $4 \times 10^{-5} \ M$ to $10^{-5} \ M$ in $100 \ mL$ solution,if $K_{sp}$ for $AgCl$ is $10^{-10} \ M^2$ at $25 \ ^oC$.

Solubility of a salt $A_2B_3$ is $1 \times 10^{-3} \ mol \ dm^{-3}$. What is the value of its solubility product?

The solubility product of lead bromide is $8 \times 10^{-5}$. If the salt is $80\%$ dissociated in a saturated solution,find the solubility of the salt.

The solubility product constant $K_{sp}$ of $Mg(OH)_2$ is $9.0 \times 10^{-12}.$ If a solution is $0.010 \ M$ with respect to $Mg^{2+}$ ion,what is the maximum hydroxide ion concentration which could be present without causing the precipitation of $Mg(OH)_2$?