Which compound does not dissolve in hot dil. `HNO_3`?

Options

A. CdS
B. CuS
C. PbS
D. HgS

Answer

To determine which compound does not dissolve in hot dilute HNO₃ (nitric acid), we will analyze the behavior of each given compound when reacted with the acid.

### Step-by-Step Solution:

1. **Identify the Compounds**: We have four compounds to consider:
- Cadmium Sulfide (CdS)
- Copper Sulfide (CuS)
- Lead Sulfide (PbS)
- Mercury Sulfide (HgS)

2. **Reactions with Hot Dilute HNO₃**:
- **Cadmium Sulfide (CdS)**:
- Reaction:
\[ 3 \text{CdS} + 8 \text{HNO}_3 \rightarrow 3 \text{Cd(NO}_3\text{)}_2 + 2 \text{NO} + 3 \text{S} + 4 \text{H}_2\text{O} \]
- Conclusion: CdS dissolves in hot dilute HNO₃.

- **Copper Sulfide (CuS)**:
- Reaction:
\[ 3 \text{CuS} + 8 \text{HNO}_3 \rightarrow 3 \text{Cu(NO}_3\text{)}_2 + 2 \text{NO} + 3 \text{S} + 4 \text{H}_2\text{O} \]
- Conclusion: CuS dissolves in hot dilute HNO₃.

- **Lead Sulfide (PbS)**:
- Reaction:
\[ 3 \text{PbS} + 8 \text{HNO}_3 \rightarrow 3 \text{Pb(NO}_3\text{)}_2 + 2 \text{NO} + 3 \text{S} + 4 \text{H}_2\text{O} \]
- Conclusion: PbS dissolves in hot dilute HNO₃.

- **Mercury Sulfide (HgS)**:
- Reaction:
- HgS does not react with hot dilute HNO₃ and remains insoluble.
- Conclusion: HgS does not dissolve in hot dilute HNO₃.

3. **Final Conclusion**: Among the given compounds, only Mercury Sulfide (HgS) does not dissolve in hot dilute HNO₃. Therefore, the correct answer is option 4.