Which one of the following
does not produce `O_2` as the only
gaseous product on heating

Options

A. Lead nitrate
B. Potassium chlorate
C. Mercuric oxide
D. Potassium nitrate

Explanation

To determine which compound does not produce O₂ as the only gaseous product upon heating, we will analyze the decomposition reactions of the given compounds one by one.

### Step-by-Step Solution:

1. **Lead Nitrate (Pb(NO₃)₂)**:
- When lead nitrate is heated, it decomposes according to the following reaction:
\[ 2 \text{Pb(NO}_3\text{)}_2 \rightarrow 2 \text{PbO} + 4 \text{NO}_2 + \text{O}_2 \]
- Products: Lead oxide (PbO), nitrogen dioxide (NO₂), and oxygen (O₂).
- **Conclusion**: This produces O₂ along with NO₂, so it does not meet the criteria.

2. **Potassium Chlorate (KClO₃)**:
- The decomposition of potassium chlorate upon heating is represented by:
\[ 2 \text{KClO}_3 \rightarrow 2 \text{KCl} + 3 \text{O}_2 \]
- Products: Potassium chloride (KCl) and oxygen (O₂).
- **Conclusion**: This produces O₂ as the only gaseous product.

3. **Mercury(II) Chloride (HgCl₂)**:
- When mercury(II) chloride is heated, it decomposes as follows:
\[ \text{HgCl}_2 \rightarrow \text{Hg} + \text{Cl}_2 \]
- Products: Mercury (Hg) and chlorine gas (Cl₂).
- **Conclusion**: This does not produce O₂ at all.

4. **Potassium Nitrate (KNO₃)**:
- The decomposition of potassium nitrate when heated is given by:
\[ 2 \text{KNO}_3 \rightarrow 2 \text{KNO}_2 + \text{O}_2 \]
- Products: Potassium nitrite (KNO₂) and oxygen (O₂).
- **Conclusion**: This produces O₂ as the only gaseous product.

### Final Answer:
The compound that does not produce O₂ as the only gaseous product upon heating is **Mercury(II) Chloride (HgCl₂)**.

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