Which of the following sulphides do not dissolve in `50% HNO_(3)` but dissolve in aquaregia ?

Options

A. `CoS`
B. `NiS`
C. `CuS`
D. `HgS`

Explanation

To solve the question of which sulphides do not dissolve in 50% HNO3 but dissolve in aqua regia, we will analyze each sulphide provided in the options.

### Step-by-Step Solution:

1. **Identify the Sulphides**: We need to evaluate the solubility of the following sulphides in 50% HNO3 and aqua regia:
- Cobalt Sulphide (CoS)
- Nickel Sulphide (NiS)
- Copper Sulphide (CuS)
- Mercury Sulphide (HgS)

2. **Evaluate Cobalt Sulphide (CoS)**:
- **In 50% HNO3**: Cobalt sulphide does not dissolve in 50% HNO3.
- **In Aqua Regia**: Cobalt sulphide dissolves in aqua regia, forming Co²⁺ ions, along with other products.
- **Conclusion**: CoS does not dissolve in 50% HNO3 but dissolves in aqua regia.

3. **Evaluate Nickel Sulphide (NiS)**:
- **In 50% HNO3**: Nickel sulphide also does not dissolve in 50% HNO3.
- **In Aqua Regia**: Nickel sulphide dissolves in aqua regia, producing Ni²⁺ ions and other products.
- **Conclusion**: NiS does not dissolve in 50% HNO3 but dissolves in aqua regia.

4. **Evaluate Copper Sulphide (CuS)**:
- **In 50% HNO3**: Copper sulphide does dissolve in 50% HNO3, producing copper nitrate and other products.
- **In Aqua Regia**: It also dissolves in aqua regia, but since it dissolves in 50% HNO3, it does not meet the criteria.
- **Conclusion**: CuS dissolves in 50% HNO3.

5. **Evaluate Mercury Sulphide (HgS)**:
- **In 50% HNO3**: Mercury sulphide does not dissolve in 50% HNO3.
- **In Aqua Regia**: Mercury sulphide dissolves in aqua regia, forming Hg²⁺ ions and other products.
- **Conclusion**: HgS does not dissolve in 50% HNO3 but dissolves in aqua regia.

6. **Final Evaluation**:
- The sulphides that do not dissolve in 50% HNO3 but dissolve in aqua regia are:
- Cobalt Sulphide (CoS)
- Nickel Sulphide (NiS)
- Mercury Sulphide (HgS)

### Answer:
The sulphides that do not dissolve in 50% HNO3 but dissolve in aqua regia are **Cobalt Sulphide (CoS), Nickel Sulphide (NiS), and Mercury Sulphide (HgS)**.