On decreasing the $p \mathrm{H}$ from $7$ to $2$ , the solubility of a sparingly soluble salt ($MX$) of a weak acid ($HX$) increased from $10^{-4} \mathrm{~mol} \mathrm{~L}^{-1}$ to $10^{-3} \mathrm{~mol} \mathrm{~L}^{-1}$. The $p \mathrm{~K}_{\mathrm{s}}$ of $\mathrm{HX}$ is:

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

The ${K_{sp}}$ of $AgCl$ is $1.0 \times {10^{ – 10}}$ calculate solubility of $AgCl$ in $0.2$ $M$ $AgN{O_3}$.

Which hydroxide will have lowest value of solubility product at normal temperature $({25\,^o}C)$

Why only $As^{3+}$ gets precipitated as $As_2S_3$ and not $Zn^{2+}$ as $ZnS$ when $H_2S$ is passed through an acidic solution containing $As^{3+}$ and $Zn^{2+}$?