Solubility product constant $\left(K_{\mathrm{sp}}\right)$ of salts of types $M X, M X_2$ and $M_3 X$ at…
Solubility product constant $\left(K_{\mathrm{sp}}\right)$ of salts of types $M X, M X_2$ and $M_3 X$ at temperature ' $T$ ' are $4.0 \times 10^{-8}, 3.2 \times 10^{-14}$ and $2.7 \times 10^{-15}$, respectively. Solubilities $\left(\mathrm{mol} \mathrm{dm}^{-3}\right)$ of the salts at temperature ' $T$ ' are in the order
$M X>M X_2>M_3 X$
$M_3 X>M X_2>M X$
$M X_2>M_3 X < M X$
$M X>M_3 X>M X_2$
Solution
$\begin{array}{lcl}\text { Salt } & \text { Solubility product } & \text { Solubility } \\ M X & S_1^2=4.0 \times 10^{-8} & S_1=2 \times 10^{-4} \\ M X_2 & 4 S_2^3=3.2 \times 10^{-14} & S_2=2 \times 10^{-5} \\ M_3 X & 27 S_3^4=2.7 \times 10^{-15} & S_3=1 \times 10^{-4}\end{array}$
Thus, solubility order $=M X>M_3 X>M X_2$.