# The only cations present in a slightly acidic solution are $Fe^{3+}, Zn^{2+}$ and $Cu^{2+}$. The reagent that when added in excess to this solution would identify and separate $Fe^{3+}$ in one step is

(a) 2M HCl
(b) 6M $NH_3$
(c) 6M $NaOH$
(d) $H_2S$ gas

Answer: 6M $NH_3$
$Fe^{3+} + Zn^{2+} + Cu^{2+} \xrightarrow{\text{6M } NH_3} Fe(OH)_3 \text{(brown ppt.)} + [Zn(NH_3)_4]^{2+} + [Cu(NH_3)_4]^{2+}$
6M $NH_3$ is used as a reagent.