Which of the following is the least soluble carbonate?

If $H_2S$ is passed in a solution of $0.1 \ M \ Zn^{2+}$ and $0.01 \ M \ Cu^{+}$ and the concentration of $S^{2-}$ is made $8.1 \times 10^{-31} \ M$. Which precipitation of $ZnS$ and $CuS$ will take place? Given: $K_{sp}(ZnS) = 3.0 \times 10^{-23}$ and $K_{sp}(CuS) = 8.0 \times 10^{-34}$.

At $T$ $K$,the solubility product of $AX$ is $10^{-10}$. What is the molar solubility of $AX$ in $0.1$ $M$ $HX$ solution?

If the solubility product constant $(K_{sp})$ of $Ni(OH)_2$ is $1.9 \times 10^{-15}$,the molar solubility of $Ni(OH)_2$ in $1.0 \ M \ NaOH$ is:

Calculate the equilibrium concentration of $Pb^{2+}$ ions in a solution of $PbS$ containing $1 \times 10^{-11} \ mol \ dm^{-3}$ of sulphide ions. (Given $K_{sp}$ for $PbS = 8.0 \times 10^{-28}$)

Assign $A, B, C, D$ from the given type of reaction.
$FeS \downarrow + 2HCl \longrightarrow FeCl_2 + H_2S \uparrow$