Which of the following reagent can dissolves precipitate of `HgSdarr`

Options

A. `NH_(3)` solution
B. conc. HCl
C. conc. `HNO_(3)`
D. `Na_(2)S` solution

Explanation

To determine which reagent can dissolve the precipitate of HgS (mercury(II) sulfide), we will analyze each of the given options step by step.

### Step-by-Step Solution:

1. **Understanding the Precipitate**:
- HgS is a black precipitate formed from the reaction of mercury ions (Hg²⁺) with sulfide ions (S²⁻).

2. **Option 1: NH3 Solution**:
- When HgS reacts with NH3, it does not dissolve. Instead, it remains as a precipitate.
- **Reaction**: HgS + NH3 → No reaction (precipitate remains).
- **Conclusion**: This option is incorrect.

3. **Option 2: Concentrated HCl**:
- When HgS is treated with concentrated HCl, it reacts to form HgCl2 and H2S, but HgS remains as a precipitate.
- **Reaction**: HgS + 2HCl → HgCl2 + H2S (precipitate remains).
- **Conclusion**: This option is incorrect.

4. **Option 3: Concentrated HNO3**:
- Concentrated HNO3 reacts with HgS to form mercury(II) nitrate, sulfuric acid, and nitrogen dioxide, but HgS remains as a precipitate.
- **Reaction**: 3HgS + 8HNO3 → 3Hg(NO3)2 + 2H2SO4 + 4NO2 + 4H2O (precipitate remains).
- **Conclusion**: This option is incorrect.

5. **Option 4: Na2S Solution**:
- When HgS is treated with Na2S, it forms a soluble complex, Na2HgS2, which indicates that HgS can dissolve in this solution.
- **Reaction**: HgS + Na2S → Na2HgS2 (HgS dissolves).
- **Conclusion**: This option is correct.

### Final Answer:
The reagent that can dissolve the precipitate of HgS is **Na2S solution**.