Chlorine gas is not produced by heating:

Options

A. `SOCl_(2)`
B. `PbCl_(4)`
C. `FeCl_(3)`
D. `Hg_(2)Cl_(2)`

Explanation

To determine which compound does not produce chlorine gas upon heating, we will analyze each option provided in the question one by one.

### Step-by-Step Solution:

1. **Analyze the first compound: COCl2 (Phosgene)**
- When COCl2 is heated, it decomposes to produce CO (carbon monoxide) and Cl2 (chlorine gas).
- **Reaction**:
\[ \text{COCl}_2 \rightarrow \text{CO} + \text{Cl}_2 \]
- **Conclusion**: COCl2 produces chlorine gas upon heating.

2. **Analyze the second compound: PbCl4 (Lead(IV) Chloride)**
- When PbCl4 is heated, it decomposes into PbCl2 (Lead(II) Chloride) and Cl2 (chlorine gas).
- **Reaction**:
\[ \text{PbCl}_4 \rightarrow \text{PbCl}_2 + \text{Cl}_2 \]
- **Conclusion**: PbCl4 also produces chlorine gas upon heating.

3. **Analyze the third compound: FeCl3 (Iron(III) Chloride)**
- When FeCl3 is heated, it decomposes into FeCl2 (Iron(II) Chloride) and Cl2 (chlorine gas).
- **Reaction**:
\[ \text{FeCl}_3 \rightarrow \text{FeCl}_2 + \text{Cl}_2 \]
- **Conclusion**: FeCl3 produces chlorine gas upon heating.

4. **Analyze the fourth compound: Hg2Cl2 (Mercury(I) Chloride)**
- When Hg2Cl2 is heated, it decomposes into mercury (Hg) and HgCl2 (Mercury(II) Chloride), but does not produce Cl2 gas.
- **Reaction**:
\[ \text{Hg}_2\text{Cl}_2 \rightarrow 2\text{Hg} + \text{HgCl}_2 \]
- **Conclusion**: Hg2Cl2 does not produce chlorine gas upon heating.

### Final Answer:
The compound that does not produce chlorine gas upon heating is **Hg2Cl2**.

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