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 the behavior of each salt in the presence of H₂S.

### Step-by-Step Solution:

1. **Identify the Salts**: We need to consider the salts mentioned in the question. The common salts that produce black precipitates with H₂S include copper sulfate (CuSO₄), lead chloride (PbCl₂), cadmium sulfate (CdSO₄), and nickel sulfate (NiSO₄).

2. **Reactions with H₂S**:
- **Copper Sulfate (CuSO₄)**: When H₂S is passed through an aqueous solution of copper sulfate, it reacts to form copper sulfide (CuS), which is a black precipitate.
\[ \text{CuSO}_4 + \text{H}_2\text{S} \rightarrow \text{CuS (black ppt)} + \text{H}_2\text{SO}_4 \]

- **Lead Chloride (PbCl₂)**: Similarly, lead chloride reacts with H₂S to form lead sulfide (PbS), which is also a black precipitate.
\[ \text{PbCl}_2 + \text{H}_2\text{S} \rightarrow \text{PbS (black ppt)} + \text{HCl} \]

- **Cadmium Sulfate (CdSO₄)**: Cadmium sulfate reacts with H₂S to produce cadmium sulfide (CdS), which is a yellow precipitate, not black.
\[ \text{CdSO}_4 + \text{H}_2\text{S} \rightarrow \text{CdS (yellow ppt)} + \text{H}_2\text{SO}_4 \]

- **Nickel Sulfate (NiSO₄)**: Nickel sulfate reacts with H₂S to form nickel sulfide (NiS), which is a black precipitate.
\[ \text{NiSO}_4 + \text{H}_2\text{S} \rightarrow \text{NiS (black ppt)} + \text{H}_2\text{SO}_4 \]

3. **Conclusion**: Among the salts mentioned, cadmium sulfate (CdSO₄) is the only salt that does not produce a black precipitate when H₂S is passed through its aqueous solution. Instead, it produces a yellow precipitate of cadmium sulfide (CdS).

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