Which of the following oxide will produce hydrogen peroxide on treatment with water ?

Options

A. `KClO_3`
B. `Na_2O_2`
C. `CaO`
D. `SO_3`

Explanation

To determine which oxide produces hydrogen peroxide (H2O2) when treated with water, we will analyze each given oxide and its reaction with water.

### Step-by-Step Solution:

1. **Identify the oxides provided**: The question mentions several oxides, including KClO3, Na2O2, CaO, and SO3.

2. **Analyze KClO3**:
- When potassium chlorate (KClO3) reacts with water, it forms potassium perchlorate (KClO4) and does not produce hydrogen peroxide.
- **Reaction**:
\[ 2 \text{KClO}_3 + 2 \text{H}_2\text{O} \rightarrow 2 \text{KClO}_4 + \text{H}_2 \]
- **Conclusion**: KClO3 does not produce H2O2. **(Incorrect option)**

3. **Analyze Na2O2**:
- Sodium peroxide (Na2O2) reacts with water to produce sodium hydroxide (NaOH) and hydrogen peroxide (H2O2).
- **Reaction**:
\[ \text{Na}_2\text{O}_2 + 2 \text{H}_2\text{O} \rightarrow 2 \text{NaOH} + \text{H}_2\text{O}_2 \]
- **Conclusion**: Na2O2 produces H2O2. **(Correct option)**

4. **Analyze CaO**:
- Calcium oxide (CaO) reacts with water to form calcium hydroxide (Ca(OH)2).
- **Reaction**:
\[ \text{CaO} + \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 \]
- **Conclusion**: CaO does not produce H2O2. **(Incorrect option)**

5. **Analyze SO3**:
- Sulfur trioxide (SO3) reacts with water to form sulfuric acid (H2SO4).
- **Reaction**:
\[ \text{SO}_3 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{SO}_4 \]
- **Conclusion**: SO3 does not produce H2O2. **(Incorrect option)**

### Final Conclusion:
The oxide that produces hydrogen peroxide when treated with water is **Na2O2**.