A very dilute acidic solution of `Cd^(2+) and Ni^(2+)` gives only yellow ppt. of CdS on passing `H_(2)S`, this is due to

Options

A. Solubility product `(K_(sp))` of CdS is more than that of NiS
B. Solubility product `(K_(sp))` of CdS is less than that of NiS
C. `Cd^(2+)` belongs to `II B` group while `Ni^(2+)` belongs to `IV^(th)` group
D. CdS is insoluble in yellow ammonium sulphide (YAS)

Explanation

To solve the problem, we need to analyze why a very dilute acidic solution containing both `Cd^(2+)` and `Ni^(2+)` gives only a yellow precipitate of `CdS` when `H2S` is passed through it.

### Step-by-Step Solution:

1. **Identify the Ions Present**:
- The solution contains `Cd^(2+)` (cadmium ions) and `Ni^(2+)` (nickel ions).

2. **Understanding the Reaction with H2S**:
- When `H2S` is passed through the solution, it provides `S^(2-)` ions which can react with the metal cations to form metal sulfides.
- The sulfides formed are `CdS` and `NiS`.

3. **Precipitation of Metal Sulfides**:
- `CdS` is known to form a yellow precipitate, while `NiS` forms a black precipitate.
- The observation states that only a yellow precipitate of `CdS` is formed.

4. **Solubility Product (Ksp) Consideration**:
- The formation of a precipitate depends on the solubility product constant (Ksp) of the metal sulfides.
- The Ksp for `CdS` is significantly lower than that of `NiS`, indicating that `CdS` is less soluble than `NiS`.

5. **Concentration of Sulfide Ions**:
- The concentration of sulfide ions required to precipitate `CdS` is lower than that required for `NiS` due to the difference in their Ksp values.
- Therefore, at a lower concentration of sulfide ions, `CdS` will precipitate first before `NiS`.

6. **Conclusion**:
- Since the solution is very dilute and both `Cd^(2+)` and `Ni^(2+)` are present in similar concentrations, the lower Ksp of `CdS` means it will precipitate first when `H2S` is introduced, leading to the formation of the yellow precipitate.

7. **Final Statement**:
- The reason why only a yellow precipitate of `CdS` is formed is that the solubility product (Ksp) of `CdS` is less than that of `NiS`, allowing `CdS` to precipitate at lower concentrations of sulfide ions.