Which of the following salt will not produce black ppt on passing `H_2S` through their aqueous salt solutions in desired medium?

Options

A. `CuSO_4`
B. `PbCl_2`
C. `CdSO_4`
D. `NiCl_2`

Answer

To solve the question of which salt will not produce a black precipitate when passing H₂S through their aqueous solutions, we can analyze each given salt one by one.

### Step-by-step Solution:

1. **Identify the salts**: The salts given are CuSO₄ (Copper sulfate), PbCl₂ (Lead chloride), CdSO₄ (Cadmium sulfate), and NiCl₂ (Nickel chloride).

2. **Understand the reaction with H₂S**: When hydrogen sulfide (H₂S) is passed through the aqueous solutions of these salts, it reacts to form metal sulfides. Some of these metal sulfides are known to produce black precipitates.

3. **Analyze each salt**:
- **CuSO₄ (Copper sulfate)**:
- Reaction: CuSO₄ + H₂S → CuS (s) + H₂SO₄
- CuS (Copper sulfide) is a black precipitate.

- **PbCl₂ (Lead chloride)**:
- Reaction: PbCl₂ + H₂S → PbS (s) + HCl
- PbS (Lead sulfide) is also a black precipitate.

- **CdSO₄ (Cadmium sulfate)**:
- Reaction: CdSO₄ + H₂S → CdS (s) + H₂SO₄
- CdS (Cadmium sulfide) is a yellow precipitate, not black.

- **NiCl₂ (Nickel chloride)**:
- Reaction: NiCl₂ + H₂S → NiS (s) + HCl
- NiS (Nickel sulfide) is a black precipitate.

4. **Conclusion**: Among the salts analyzed, CdSO₄ (Cadmium sulfate) does not produce a black precipitate; instead, it produces a yellow precipitate (CdS).

### Final Answer:
The salt that will not produce a black precipitate on passing H₂S through its aqueous solution is **CdSO₄ (Cadmium sulfate)**.