The compound which gives off oxygen on moderate heating is

Options

A. cupric oxide
B. mercuric oxide
C. zinc oxide
D. aluminium oxide

Explanation

To determine which compound gives off oxygen upon moderate heating, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Analyze the First Option: Cupric Oxide (CuO)**
- When cupric oxide is heated, it does not release oxygen. Instead, it can be reduced to cuprous oxide (Cu2O) under certain conditions.
- **Conclusion**: Cupric oxide does not give off oxygen upon heating.

2. **Analyze the Second Option: Mercuric Oxide (HgO)**
- When mercuric oxide is heated, it decomposes into mercury (Hg) and oxygen (O2).
- The balanced chemical equation for this reaction is:
\[ 2 \, \text{HgO} \rightarrow 2 \, \text{Hg} + \text{O}_2 \]
- **Conclusion**: Mercuric oxide does release oxygen upon moderate heating.

3. **Analyze the Third Option: Zinc Oxide (ZnO)**
- When zinc oxide is heated at high temperatures (around 800 °C), it does not release oxygen. Instead, it can form a non-stoichiometric compound (ZnOx) where x is less than 1, but this does not involve the release of oxygen.
- **Conclusion**: Zinc oxide does not give off oxygen.

4. **Analyze the Fourth Option: Aluminium Oxide (Al2O3)**
- Aluminium oxide does not release oxygen upon heating. To remove oxygen from aluminium oxide, a reducing agent is required, and this is done through a process known as the Hall-Héroult process.
- **Conclusion**: Aluminium oxide does not give off oxygen.

### Final Answer:
After analyzing all the options, the compound that gives off oxygen upon moderate heating is **Mercuric Oxide (HgO)**.

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