Oxygen is not evolved in a reaction between

Options

A. `NaNO_2 + O_3`
B. `As + O_3`
C. `SO_2 + O_3`
D. `Hg + O_3`

Explanation

To solve the question "Oxygen is not evolved in a reaction between," we need to analyze various reactions involving ozone (O3) and other compounds to determine which one does not produce oxygen gas (O2) as a product.

### Step-by-Step Solution:

1. **Identify the Reactions**: We will consider several reactions involving ozone and other compounds to see if oxygen is produced.

2. **First Reaction**:
- **NaNO2 + O3 → NaNO3 + O2**
- In this reaction, sodium nitrite (NaNO2) reacts with ozone (O3) to produce sodium nitrate (NaNO3) and oxygen gas (O2).
- **Conclusion**: Oxygen is evolved.

3. **Second Reaction**:
- **As + O3 → As2O3 + O2**
- Here, arsenic (As) reacts with ozone (O3) to form arsenic oxide (As2O3) and oxygen gas (O2).
- **Conclusion**: Oxygen is evolved.

4. **Third Reaction**:
- **SO2 + O3 → SO3 + O2**
- In this reaction, sulfur dioxide (SO2) reacts with ozone (O3) to produce sulfur trioxide (SO3) and oxygen gas (O2).
- **Conclusion**: Oxygen is evolved.

5. **Fourth Reaction**:
- **H2O + SO2 + O3 → H2SO4**
- When water (H2O) and sulfur dioxide (SO2) react with ozone (O3), they form sulfuric acid (H2SO4). In this case, oxygen is not released as a product.
- **Conclusion**: Oxygen is not evolved.

6. **Fifth Reaction**:
- **Hg + O3 → HgO + O2**
- In this reaction, mercury (Hg) reacts with ozone (O3) to produce mercury oxide (HgO) and oxygen gas (O2).
- **Conclusion**: Oxygen is evolved.

7. **Final Conclusion**:
- Among all the reactions analyzed, the reaction between **SO2 and O3** does not produce oxygen gas. Therefore, the correct answer to the question is the reaction **SO2 + O3**.

### Answer:
**Oxygen is not evolved in the reaction between SO2 and O3.**