The only cations present in a slightly acidic solution are `Fe^(3+),Zn^(2+)` and `Cu^(2+)` . The regent that when added in excess to this solution would identify and separate `Fe^(3+)` in one step is
A. 2 M HCl
B. 6 M `NH_(3)`
C. 6 M NaOH
D. `H_(2)S` gas