Which of the following pairs of ions when mixed in dilute solutions may give a precipitate?

The solubility of a sparingly soluble salt $AB_2$ is $1 \times 10^{-6} \text{ mol/dm}^3$. Calculate its solubility product.

Two salts $A_2X$ and $MX$ have the same value of solubility product of $4.0 \times 10^{-12}$. The ratio of their molar solubilities i.e. $\frac{S(A_2X)}{S(MX)} = \dots$ (Round off to the Nearest Integer).

The solubility of $PbI_2$ at $25\,^{\circ}C$ is $0.7\, g\, L^{-1}$. The solubility product of $PbI_2$ at this temperature is (molar mass of $PbI_2 = 461.2\, g\, mol^{-1}$)

The $K_{sp}$ of $Mg(OH)_2$ is $1.0 \times 10^{-12}$. At which $pH$ does $0.01 \ M$ $Mg^{2+}$ solution begin to precipitate? Calculate the solubility of $Mg(OH)_2$ in pure water.

When equal volumes of the following solutions are mixed,precipitation of $AgCl$ will occur in - ($K_{sp}$ of $AgCl = 1.8 \times 10^{-10}$)