Which one among the following pairs of ions cannot be separated by `H_2 S` in dilute hydrochloric acid?

Options

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

Answer

A

Explanation

Both `Bi^(3+)` and `Cu^(2+)` will be precipitated as `Bi_2S_3`(black) and CdS (yellow) by `H_2S` as both have low values of `K_(sp)` then `Al^(3+)` , `Zn^(2+) and Ni^(2+)` (as sulphides)