Which cannot be oxidised by `H_(2)O_(2)` ?

Options

A. `Na_(2)SO_(3)`
B. `MnSO_4`
C. `FeSO_4`
D. o3

Answer

To determine which substance cannot be oxidized by hydrogen peroxide (H₂O₂), we need to analyze the oxidation states of the elements in the given options and understand the oxidizing properties of H₂O₂.

### Step-by-Step Solution:

1. **Understanding Hydrogen Peroxide as an Oxidizing Agent**:
- Hydrogen peroxide (H₂O₂) is known to be a strong oxidizing agent. It can decompose to produce nascent oxygen, which is capable of oxidizing various substances.

2. **Analyzing the Options**:
- We need to evaluate each option to see if it can be oxidized by H₂O₂.

3. **Option A: SO₃²⁻ (Sulfite Ion)**:
- The oxidation state of sulfur in SO₃²⁻ is +4.
- It can be oxidized to SO₄²⁻ (sulfate ion), where the oxidation state of sulfur is +6.
- Therefore, H₂O₂ can oxidize SO₃²⁻.

4. **Option B: MnSO₄ (Manganese(II) Sulfate)**:
- The oxidation state of manganese (Mn) in MnSO₄ is +2.
- It can be oxidized to MnO₄⁻ (permanganate ion), where the oxidation state of Mn is +7.
- Hence, H₂O₂ can oxidize MnSO₄.

5. **Option C: Ferrous Ion (Fe²⁺)**:
- The oxidation state of iron (Fe) in ferrous ion is +2.
- It can be oxidized to ferric ion (Fe³⁺), where the oxidation state of Fe is +3.
- Thus, H₂O₂ can oxidize Fe²⁺.

6. **Option D: Ozone (O₃)**:
- Ozone is a powerful oxidizing agent itself.
- Since H₂O₂ is less powerful than ozone, it cannot oxidize ozone. Instead, ozone can act as an oxidizing agent and may reduce H₂O₂.
- Therefore, H₂O₂ cannot oxidize O₃.

7. **Conclusion**:
- The substance that cannot be oxidized by H₂O₂ is **Option D: Ozone (O₃)**.

### Final Answer:
**Option D: Ozone (O₃)** cannot be oxidized by H₂O₂.