Oxygen is not evolved when:

Options

A. potassium chlorate is heated with `MnO_(2)` catalyst
B. sodium peroxide reacts with water
C. ammonium nitrate is heated
D. zinc oxide is treated with NaOH

Explanation

To determine when oxygen is not evolved, we will analyze each option provided in the question step by step.

### Step-by-Step Solution:

1. **Option 1: Potassium chlorate (KClO3) heated with MnO2 catalyst**
- When potassium chlorate is heated in the presence of manganese dioxide (MnO2), it decomposes to form potassium chloride (KCl) and oxygen gas (O2).
- **Reaction:**
\[ 2 KClO_3 \xrightarrow{MnO_2} 2 KCl + 3 O_2 \]
- **Conclusion:** Oxygen is evolved in this reaction.

2. **Option 2: Sodium peroxide (Na2O2) reacts with water**
- Sodium peroxide reacts with water to produce sodium hydroxide (NaOH) and oxygen gas (O2).
- **Reaction:**
\[ Na_2O_2 + 2 H_2O \rightarrow 2 NaOH + O_2 \]
- **Conclusion:** Oxygen is evolved in this reaction.

3. **Option 3: Ammonium nitrate (NH4NO3) is heated**
- When ammonium nitrate is heated, it decomposes to form nitrous oxide (N2O) and water (H2O).
- **Reaction:**
\[ 2 NH_4NO_3 \rightarrow N_2O + 2 H_2O \]
- **Conclusion:** Oxygen is not evolved in this reaction.

4. **Option 4: Zinc oxide (ZnO) treated with NaOH**
- When zinc oxide is treated with sodium hydroxide, it forms sodium zincate (Na2ZnO2) and water (H2O). There is no evolution of oxygen in this reaction.
- **Reaction:**
\[ ZnO + 2 NaOH \rightarrow Na_2ZnO_2 + H_2O \]
- **Conclusion:** Oxygen is not evolved in this reaction.

### Final Conclusion:
From the analysis:
- **Oxygen is evolved:** Option 1 and Option 2.
- **Oxygen is not evolved:** Option 3 and Option 4.

Thus, the final answer is that oxygen is not evolved when:
- **Option 3: Ammonium nitrate is heated.**
- **Option 4: Zinc oxide is treated with NaOH.**