`H_(2)O_(2)` acts as a reducing agent in

Options

A. `Na_(2)S+4H_(2)O_(2)rarr Na_(2)SO_(4)+4H_(2)O`
B. `Mn^(2+)+2H_(2)O_(2)rarr MnO_(2)+2H_(2)O`
C. `2Fe^(2+)+2H^(+)+H_(2)O_(2)rarr2Fe^(3+)+2H_(2)O`
D. `2NaOCI + H_2O_2 to 2 NaCl + H_2O +O_2`

Answer

To determine in which reaction H₂O₂ (hydrogen peroxide) acts as a reducing agent, we need to analyze the oxidation states of the elements involved in each reaction. A reducing agent is a substance that donates electrons (and thus gets oxidized) during a chemical reaction.

### Step-by-Step Solution:

1. **Identify the Oxidation State of Oxygen in H₂O₂**:
- In H₂O₂, the oxidation state of oxygen is -1.

2. **Analyze the Reactions**:
- We have four reactions to analyze. We will check the oxidation states of oxygen in the other species involved in each reaction to see if H₂O₂ is oxidized (which would mean it acts as a reducing agent).

3. **Reaction 1**:
- If H₂O₂ is reacting with a species where oxygen is in a lower oxidation state (like -2), H₂O₂ cannot act as a reducing agent because it would not be oxidized.
- Check the oxidation states of the other reactants and products. If H₂O₂ remains at -1, it is not acting as a reducing agent.

4. **Reaction 2**:
- Repeat the same process as in Reaction 1. Check if H₂O₂ is oxidized (the oxidation state of oxygen increases) or remains the same. If it does not oxidize, it is not a reducing agent.

5. **Reaction 3**:
- Again, check the oxidation states. If H₂O₂ stays at -1 while the other species are reduced, it is not acting as a reducing agent.

6. **Reaction 4**:
- In this reaction, if H₂O₂ is oxidized (the oxidation state of oxygen increases from -1 to 0 in O₂), it indicates that H₂O₂ is donating electrons and thus acting as a reducing agent.
- Here, H₂O₂ reduces NaOCl (sodium hypochlorite) to NaCl (sodium chloride) and is oxidized to O₂.

7. **Conclusion**:
- Based on the analysis, H₂O₂ acts as a reducing agent in the fourth reaction where it is oxidized from -1 to 0.

### Final Answer:
H₂O₂ acts as a reducing agent in the fourth reaction.

---