Chemistry - Salt Analysis Question with Solution | TestHub

$\begin{array}{rl}& {\mathrm{NH}}_4\mathrm{OH}\rightleftharpoons {\mathrm{NH}}_4^{+}+{\mathrm{OH}}^{-}\\ & {\mathrm{NH}}_4\mathrm{Cl}\to {\mathrm{NH}}_4^{+}+\mathrm{Cl}\end{array}$
Due to common ion effect of ${\mathrm{NH}}_4^{+}$, $\left[{\mathrm{OH}}^{-}\right]$decreases in such extent that only group-III cation can be precipitated, due to their very low ${\mathrm{K}}_{\mathrm{sp}}$ in the range of $10^{-38}$.