Which can act as a reducing agent ?

Options

A. `HNO_(3)`
B. `H_(2)SO_(4)`
C. `H_(2)S`
D. `KMnO_(4)`

Answer

To determine which of the given substances can act as a reducing agent, we need to analyze the oxidation states of the central atoms in each compound. A reducing agent is a substance that can donate electrons to another substance, causing that substance to be reduced while the reducing agent itself gets oxidized.

### Step-by-Step Solution:

1. **Identify the Compounds**: The compounds given are HNO3, H2SO4, H2S, and KMnO4.

2. **Determine the Oxidation States**:
- **HNO3**: The oxidation state of nitrogen (N) in HNO3 is +5.
- **H2SO4**: The oxidation state of sulfur (S) in H2SO4 is +6.
- **H2S**: The oxidation state of sulfur (S) in H2S is +2.
- **KMnO4**: The oxidation state of manganese (Mn) in KMnO4 is +7.

3. **Analyze the Oxidation States**:
- In HNO3, nitrogen is at its maximum oxidation state (+5), meaning it cannot act as a reducing agent.
- In H2SO4, sulfur is at +6, also indicating it cannot act as a reducing agent.
- In H2S, sulfur is at +2, which means it can lose electrons and increase its oxidation state, thus acting as a reducing agent.
- In KMnO4, manganese is at +7, which is its maximum oxidation state, so it cannot act as a reducing agent.

4. **Conclusion**: Among the given options, H2S can act as a reducing agent because it can lose electrons and increase its oxidation state.

### Final Answer:
**H2S is the only compound that can act as a reducing agent.**

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