Which of the following reagents can be used to separate $AgCl$ and $AgI$?

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

$A$ $1.0 \ L$ 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:
$(K_{sp}(AgCl) = 1.8 \times 10^{-10}; K_{sp}(AgBr) = 5 \times 10^{-13}; K_{sp}(AgI) = 8.3 \times 10^{-17})$

Sodium sulfate is soluble in water,whereas barium sulfate is sparingly soluble. Why?

Assign $A, B, C, D$ from the given type of reaction.
$2AgNO_3 + Na_2C_2O_4 \longrightarrow Ag_2C_2O_4 \downarrow + 2NaNO_3$

The molar solubility of a sparingly soluble salt $MX_4$ is $s \ mol \ L^{-1}$. If the solubility product is $K_{sp}$,then $s$ in terms of $K_{sp}$ is: