Which of the following reagents can dissolve the precipitate of $HgS\,\downarrow$?

Calculate the minimum concentration of sulphate ion required to precipitate $BaSO_4$ in a solution containing $10^{-4} \ mol/L$ of $Ba^{2+}$. $(K_{sp} \ BaSO_4 = 4 \times 10^{-10})$

The molar solubility $(s)$ of zirconium phosphate with molecular formula $(Zr^{4+})_3(PO_4^{3-})_4$ is given by the relation:

The solubility of sparingly soluble salt $AB_2$ is $1.0 \times 10^{-4} \ mol \ dm^{-3}$. What is its solubility product?

At $25\,^{\circ}C$,the solubility product of $Mg(OH)_2$ is $1.0 \times 10^{-11}$. At which $pH$ will $Mg^{2+}$ ions start precipitating in the form of $Mg(OH)_2$ from a solution of $0.001\, M\, Mg^{2+}$ ions?

How many grams of $CaC_2O_4$ will dissolve in distilled water to make one litre of saturated solution (in $g$)? (Solubility product of $CaC_2O_4$ is $2.5 \times 10^{-9} \ mol^2 \ L^{-2}$ and its molecular weight is $128$)