`H_(2)O_(2)` cannot oxidise :

Options

A. KI
B. PbS
C. `O_(3)`
D. `Na_(2)SO_(3)`

Explanation

To determine which substance hydrogen peroxide (H₂O₂) cannot oxidize, we need to analyze the oxidation states of the elements involved in the reactions with various substances.

### Step-by-Step Solution:

1. **Understanding Oxidation**:
- Oxidation is defined as the process where the oxidation state of an element increases. This can occur when an element loses electrons or when it combines with oxygen.

2. **Analyzing Reactions**:
- We will look at the reactions of H₂O₂ with different substances to see if it acts as an oxidizing agent (which means it increases the oxidation state of another substance).

3. **Reaction with PbS (Lead Sulfide)**:
- **Reaction**: PbS + H₂O₂ → PbSO₄ + H₂O
- **Oxidation States**:
- In PbS, the oxidation state of S is -2.
- In PbSO₄, the oxidation state of S is +6.
- **Conclusion**: The oxidation state of sulfur increases from -2 to +6, indicating that H₂O₂ oxidizes PbS.

4. **Reaction with KI (Potassium Iodide)**:
- **Reaction**: 2KI + H₂O₂ + 2HCl → 2KCl + I₂ + 2H₂O
- **Oxidation States**:
- In KI, the oxidation state of I is -1.
- In I₂, the oxidation state of I is 0.
- **Conclusion**: The oxidation state of iodine increases from -1 to 0, indicating that H₂O₂ oxidizes KI.

5. **Reaction with Na₂SO₃ (Sodium Sulfite)**:
- **Reaction**: Na₂SO₃ + H₂O₂ → Na₂SO₄ + H₂O
- **Oxidation States**:
- In Na₂SO₃, the oxidation state of S is +4.
- In Na₂SO₄, the oxidation state of S is +6.
- **Conclusion**: The oxidation state of sulfur increases from +4 to +6, indicating that H₂O₂ oxidizes Na₂SO₃.

6. **Reaction with Ozone (O₃)**:
- **Reaction**: H₂O₂ + O₃ → Products
- **Oxidation States**:
- In ozone (O₃), the oxidation state of O is 0.
- In H₂O₂, the oxidation state of O is -1.
- **Conclusion**: Ozone is a stronger oxidizing agent than H₂O₂, and in this reaction, H₂O₂ acts as a reducing agent, reducing the oxidation state of ozone from 0 to -2.

7. **Final Conclusion**:
- H₂O₂ cannot oxidize ozone (O₃) because it acts as a reducing agent in this reaction.

### Final Answer:
H₂O₂ cannot oxidize **ozone (O₃)**.