Which of the following can be used both as an oxidant and a reductant?

Options

A. `HNO_(2)`
B. `SO_(2)`
C. `O_(2)`
D. `CO`

Explanation

To determine which of the given compounds can act both as an oxidant (oxidizing agent) and a reductant (reducing agent), we need to analyze the oxidation states of the elements in each compound.

### Step-by-Step Solution:

1. **Identify the Oxidation States**:
- For each compound, we need to identify the oxidation state of the element that can change during the redox reaction.

2. **Analyze HNO2 (Nitrous Acid)**:
- The oxidation state of nitrogen in HNO2 is +3.
- It can be oxidized to +5 (acting as a reductant) or reduced to +2 (acting as an oxidant).
- Conclusion: HNO2 can act as both an oxidant and a reductant.

3. **Analyze SO2 (Sulfur Dioxide)**:
- The oxidation state of sulfur in SO2 is +4.
- It can be oxidized to +6 (acting as a reductant) or reduced to -2 (acting as an oxidant).
- Conclusion: SO2 can act as both an oxidant and a reductant.

4. **Analyze O2 (Oxygen)**:
- The oxidation state of oxygen in O2 is 0.
- It can be reduced to -2 (acting as an oxidant) or oxidized to +2 (acting as a reductant).
- Conclusion: O2 can act as both an oxidant and a reductant.

5. **Analyze CO (Carbon Monoxide)**:
- The oxidation state of carbon in CO is +2.
- It can be oxidized to +4 (acting as a reductant) or reduced to -4 (acting as an oxidant).
- Conclusion: CO can act as both an oxidant and a reductant.

6. **Final Conclusion**:
- Since all four compounds (HNO2, SO2, O2, and CO) can act as both oxidants and reductants, the answer is that all of them can be used both as oxidants and reductants.

### Final Answer:
All of the given compounds (HNO2, SO2, O2, CO) can be used both as oxidants and reductants.

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