Which of the following reactions with $H_2S$ does not produce metallic sulphide?

The molar solubility $(mol \ L^{-1})$ of a sparingly soluble salt $MX_4$ is $s$. The corresponding solubility product is $K_{sp}$. $s$ is given in terms of $K_{sp}$ by the relation:

The concentration of a saturated solution of $Mg(OH)_2$ is $8.2 \times 10^{-4} \ g \ L^{-1}$ at $298 \ K$. Calculate its solubility product $(K_{sp})$. (Molar mass of $Mg(OH)_2 = 58 \ g \ mol^{-1}$)

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

$A$ $1.0 \ L$ of aqueous solution contains $1 \times 10^{-8} \ M \ NaBr$,$1 \times 10^{-8} \ M \ NaCl$ and $1 \times 10^{-8} \ M \ NaI$. To this solution,$1 \times 10^{-10} \ M$ aqueous $AgNO_3$ solution is added dropwise. The order of precipitation of $AgX$ $(X = Cl, Br, I)$ is:
$(K_{sp}(AgCl) = 1.8 \times 10^{-10}; K_{sp}(AgBr) = 5 \times 10^{-13}; K_{sp}(AgI) = 8.3 \times 10^{-17})$

For the precipitation reaction of $Ag^{\oplus}$ ions with $NaCl,$ which of the following statements is true?