Which of the following is least soluble in water?

The $K_{sp}$ of $AgI$ is $1.5 \times 10^{-16}$. Precipitation will occur upon mixing equal volumes of which of the following solutions?

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$Ag_2CO_3 \downarrow + 2HCl \longrightarrow 2AgCl \downarrow + CO_2 \uparrow + H_2O$

Solubility of $PbI_2$ is $0.005 \ M$. Then,the solubility product of $PbI_2$ is

Solid $Ba(NO_3)_2$ is gradually dissolved in a $1.0 \times 10^{-4} \ M$ $Na_2CO_3$ solution. At what concentration of $Ba^{2+}$ will a precipitate begin to form? ($K_{sp}$ for $BaCO_3 = 5.1 \times 10^{-9}$)

At $20 \, ^\circ C$,the concentration of $Ag^+$ ions in a saturated solution of $Ag_2CrO_4$ is $1.5 \times 10^{-4} \, M$. The solubility product $(K_{sp})$ of $Ag_2CrO_4$ at $20 \, ^\circ C$ is: