In Qualitative Inorganic Analysis, cations are separated into groups based on their solubility products ($K_{sp}$).

• Group III Cations ($F{e}^{3+},A{l}^{3+},C{r}^{3+}$) have relatively low solubility products for their hydroxides.
• Group Reagent: $N{H}_{4}OH$ in the presence of $N{H}_{4}Cl$.
• Function of $N{H}_{4}Cl$: It suppresses the ionization of $N{H}_{4}OH$ (Common Ion Effect), ensuring that the concentration of $O{H}^{-}$ ions is just enough to precipitate Group III hydroxides but not high enough to precipitate Group IV or later cations (like $M{g}^{2+}$).