Identify the compound which turns black with ammonia solution.

Options

A. Lead chloride
B. Mercurous chloride
C. Mercuric chloride
D. Silver chloride

Explanation

To identify the compound that turns black with ammonia solution, we will analyze the reactions of different compounds with ammonium hydroxide (NH4OH).

### Step-by-Step Solution:

1. **Identify the Compounds**: We will consider the following compounds:
- Lead chloride (PbCl2)
- Mercurous chloride (Hg2Cl2)
- Mercuric chloride (HgCl2)
- Silver chloride (AgCl)

2. **Reaction of Lead Chloride with Ammonium Hydroxide**:
- When lead chloride (PbCl2) is treated with ammonium hydroxide (NH4OH), it forms lead hydroxide (Pb(OH)2), which is a white precipitate.
- **Equation**:
\[ \text{PbCl}_2 + 2 \text{NH}_4\text{OH} \rightarrow \text{Pb(OH)}_2 \text{(white PPT)} + 2 \text{NH}_4\text{Cl} \]
- **Observation**: White precipitate.

3. **Reaction of Mercurous Chloride with Ammonium Hydroxide**:
- When mercurous chloride (Hg2Cl2) reacts with ammonium hydroxide, it produces mercury (Hg) and ammonium chloride (NH4Cl). The mercury formed is metallic and appears black.
- **Equation**:
\[ \text{Hg}_2\text{Cl}_2 + 2 \text{NH}_4\text{OH} \rightarrow 2 \text{Hg (black)} + 2 \text{NH}_4\text{Cl} + \text{HgCl} \]
- **Observation**: Black precipitate.

4. **Reaction of Mercuric Chloride with Ammonium Hydroxide**:
- When mercuric chloride (HgCl2) reacts with ammonium hydroxide, it forms mercury(I) amide (HgNH2) and water, which is a white precipitate.
- **Equation**:
\[ \text{HgCl}_2 + 2 \text{NH}_4\text{OH} \rightarrow \text{HgNH}_2 \text{(white PPT)} + 2 \text{H}_2\text{O} + 2 \text{HCl} \]
- **Observation**: White precipitate.

5. **Reaction of Silver Chloride with Ammonium Hydroxide**:
- When silver chloride (AgCl) reacts with ammonium hydroxide, it forms silver oxide (Ag2O) and ammonia, resulting in a brownish precipitate.
- **Equation**:
\[ 2 \text{AgCl} + 2 \text{NH}_4\text{OH} \rightarrow \text{Ag}_2\text{O (brown PPT)} + 2 \text{NH}_4\text{Cl} + 2 \text{H}_2\text{O} \]
- **Observation**: Brown precipitate.

6. **Conclusion**: Among the compounds analyzed, only mercurous chloride (Hg2Cl2) produces a black precipitate when treated with ammonium hydroxide. Therefore, the compound that turns black with ammonia solution is **mercurous chloride (Hg2Cl2)**.

### Final Answer:
The compound which turns black with ammonia solution is **mercurous chloride (Hg2Cl2)**.