JEE Chemistry 2023 Question with Solution

Given: The cations are $\mathrm{Fe}^{3+}$, $\mathrm{Zn}^{2+}$, $\mathrm{Co}^{2+}$ and $\mathrm{Ni}^{2+}$.

Find: Which cation does not belong to Group IV in qualitative inorganic analysis.

In qualitative inorganic analysis, cations are classified according to their precipitation behavior with group reagents.

Group III: includes $\mathrm{Fe}^{3+}$, $\mathrm{Al}^{3+}$ and $\mathrm{Cr}^{3+}$, which precipitate as hydroxides with $\mathrm{NH_4OH}$ and $\mathrm{NH_4Cl}$.

Group IV: includes $\mathrm{Zn}^{2+}$, $\mathrm{Co}^{2+}$ and $\mathrm{Ni}^{2+}$, which precipitate as sulfides with $\mathrm{H_2S}$.

Thus, $\mathrm{Fe}^{3+}$ belongs to Group III, not Group IV.

Therefore, the correct option is A.