Which of the following has maximum solubility at low $pH$?

Zirconium phosphate $[Zr_3(PO_4)_4]$ dissociates into three zirconium cations of charge $+4$ and four phosphate anions of charge $-3$. If molar solubility of zirconium phosphate is denoted by $S$ and its solubility product by $K_{sp}$,then which of the following relationships between $S$ and $K_{sp}$ is correct?

For the equilibrium reaction: $Fe(OH)_3(s) \rightleftharpoons Fe^{3+}(aq) + 3OH^-(aq)$,if the concentration of $OH^-$ is reduced to $\frac{1}{4}$ of its initial value,by what factor will the concentration of $Fe^{3+}$ increase at equilibrium?

If the concentration of lead iodide in its saturated solution at $25 \, ^oC$ is $2 \times 10^{-3} \ mol \ L^{-1}$,then its solubility product is:

If the concentration of $[Ag^{+}]$ in a solution is $1 \times 10^{-6} \ M$,what is the concentration of $[Br^{-}]$? Given that the $K_{sp}$ for $AgBr$ is $4.0 \times 10^{-13}$.

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 $BaCO_3 = 5.1 \times 10^{-9}$)