Cations are classified into varius group on the basis of their behaviour against some reagents .The group reagent used for the classifaction of most common cation are `HCI,H_(2)S,NH_(4)OH,(NH_(4))_(2)CO_(3)`. Classification is based on whether a cation reacts with these reagents by the formation of precipitates or not .
Which one among the following paires of ions cannot be separated by `H_(2)S` in the presence of dilute hydrochloric acid ?

Options

A. `Bi^(2+),Cd^(2+)`
B. `AI^(2+),Hg^(2+)`
C. `Zn^(3+),Cu^(2+)`
D. `Ni^(2+),Cu^(2+)`

Answer

a

Explanation

Both `Bi^(3+) and Cd^(2+)` will be precipitate in `Bi_(2)S_(3)` (black) and `CdS` (yellow) by `H_(2)S` as both low values of `K_(sp)` than `AI^(3+),Zn^(2+) and Ni^(2+)` (as sulphides)