Which of the following is a set of reducing agents :-

Options

A. `HNO_(3), Fe^(+2), Fe`
B. `F^(-) , Cl^(-), MnO_(4)^(-)`
C. `I^(-), Na, Fe^(+2)`
D. `Cr_(2) O_(7)^(-2), NaCl`

Answer

To determine which of the given options contains a set of reducing agents, we need to analyze the oxidation states of the species in each option and identify which can act as reducing agents. A reducing agent is a substance that can lose electrons and thereby increase its oxidation state.

### Step-by-Step Solution:

1. **Understanding Reducing Agents**:
- Reducing agents are substances that can be oxidized themselves, meaning their oxidation state increases during the reaction.

2. **Analyzing Option A: HNO3, Fe²⁺, Fe**:
- **HNO3**: The oxidation state of nitrogen in HNO3 is +5. Since this is the maximum oxidation state for nitrogen, it cannot act as a reducing agent.
- **Fe²⁺**: Iron in the +2 oxidation state can be oxidized to +3, thus it can act as a reducing agent.
- **Fe**: Iron in the elemental state (0 oxidation state) can be oxidized to +2 or +3, so it can also act as a reducing agent.
- **Conclusion**: HNO3 is not a reducing agent, so this option is not valid.

3. **Analyzing Option B: F⁻, Cl⁻, MnO4⁻**:
- **F⁻**: Fluoride cannot be oxidized further as it is already in its lowest oxidation state (-1).
- **Cl⁻**: Chloride can be oxidized to Cl₂ (0 oxidation state), so it can act as a reducing agent.
- **MnO4⁻**: The oxidation state of manganese in MnO4⁻ is +7, which is its maximum oxidation state, so it cannot act as a reducing agent.
- **Conclusion**: Since F⁻ and MnO4⁻ cannot act as reducing agents, this option is not valid.

4. **Analyzing Option C: I⁻, Na, Fe²⁺**:
- **I⁻**: Iodide can be oxidized to I₂ (0 oxidation state), so it can act as a reducing agent.
- **Na**: Sodium can be oxidized from 0 to +1, thus it can act as a reducing agent.
- **Fe²⁺**: As previously discussed, Fe²⁺ can be oxidized to Fe³⁺, so it can also act as a reducing agent.
- **Conclusion**: All species in this option can act as reducing agents.

5. **Analyzing Option D: Cr2O7²⁻, NaCl**:
- **Cr2O7²⁻**: The oxidation state of chromium in Cr2O7²⁻ is +6. It can be reduced to lower oxidation states, so it can act as a reducing agent.
- **NaCl**: Sodium in NaCl has an oxidation state of +1, which is its maximum oxidation state, so it cannot act as a reducing agent.
- **Conclusion**: Since NaCl cannot act as a reducing agent, this option is not valid.

### Final Conclusion:
The only valid set of reducing agents is found in **Option C: I⁻, Na, Fe²⁺**.