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

Question

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