In which one of the following reactions, hydrogen peroxide is acts as an oxidising agent ?

Options

A. (a) `HOCl+ H_(2)O_(2) to H_(3)O^(+) + Cl^(-) + O_(2)`
B. (b) `I_(2) + H_(2)O_(2) + 2OH^(-) to 2H_(2)O + O_(2)`
C. (c) `PbS + 4H_(2)O_(2) to PbSO_(4) + 4H_(2)O`
D. (d) `2MnO_(4)^(-) + 3H_(2)O_(2) to 2MnO_(2) + 3O_(2) + 2H_(2)O + 2OH^(-)`

Answer

To determine in which reaction hydrogen peroxide (H2O2) acts as an oxidizing agent, we need to analyze the oxidation states of the elements involved in each reaction. An oxidizing agent is a substance that gains electrons (is reduced) while causing another substance to lose electrons (be oxidized).

### Step-by-Step Solution:

1. **Understanding Oxidizing Agents**:
- An oxidizing agent is a substance that oxidizes another substance and itself gets reduced. This means it gains electrons.

2. **Analyzing Each Option**:
- We will evaluate each reaction option to see if H2O2 acts as an oxidizing agent.

3. **Option A: HOCl + H2O2**:
- In this reaction, chlorine (Cl) in HOCl is in the +1 oxidation state and can be reduced to -1 in Cl⁻.
- Since Cl is being reduced, H2O2 is acting as a reducing agent here, not an oxidizing agent.
- **Conclusion**: H2O2 does not act as an oxidizing agent in this reaction.

4. **Option B: I2 + H2O2**:
- In this reaction, I2 (iodine) is in the 0 oxidation state and can be reduced to -1 in I⁻.
- Since iodine is being reduced, H2O2 is again acting as a reducing agent.
- **Conclusion**: H2O2 does not act as an oxidizing agent in this reaction.

5. **Option C: PbS + H2O2**:
- In this reaction, sulfur (S) in PbS is in the -2 oxidation state and is oxidized to +6 in PbSO4.
- Since sulfur is being oxidized, H2O2 is acting as an oxidizing agent.
- **Conclusion**: H2O2 acts as an oxidizing agent in this reaction.

6. **Option D: MnO4⁻ + H2O2**:
- In this reaction, manganese (Mn) in MnO4⁻ is in the +7 oxidation state and is reduced to +4 in MnO2.
- Since manganese is being reduced, H2O2 is acting as a reducing agent.
- **Conclusion**: H2O2 does not act as an oxidizing agent in this reaction.

### Final Answer:
The correct answer is **Option C: PbS + H2O2**, where H2O2 acts as an oxidizing agent.