Which of the following can act as oxidising as well as reducing agent?

Options

A. `O_(2)`
B. `HNO_(3)`
C. `SO_(2)`
D. `H_(2)O_(2)`

Answer

To determine which of the given substances can act as both an oxidizing agent and a reducing agent, we need to analyze their oxidation states and the range of oxidation states they can exhibit.

### Step-by-Step Solution:

1. **Understanding Oxidizing and Reducing Agents**:
- An oxidizing agent is a substance that gains electrons (is reduced) and causes another substance to be oxidized.
- A reducing agent is a substance that loses electrons (is oxidized) and causes another substance to be reduced.

2. **Identifying Oxidation States**:
- We need to find the oxidation states of the elements in the given compounds: O2, HNO3, SO2, and H2O2.

3. **Analyzing Each Compound**:
- **O2**: The oxidation state of O in O2 is 0. Oxygen can have oxidation states ranging from -2 (in most compounds) to +6 (in peroxides and superoxides). Since 0 is between -2 and +6, O2 can act as both an oxidizing and reducing agent.
- **HNO3**: In HNO3, nitrogen has an oxidation state of +5. This is at the extreme limit (maximum oxidation state for nitrogen), so HNO3 cannot act as a reducing agent.
- **SO2**: In SO2, sulfur has an oxidation state of +4. The oxidation state of sulfur can range from -2 to +6, so +4 is within this range. Therefore, SO2 can act as both an oxidizing and reducing agent.
- **H2O2**: In H2O2, the oxidation state of oxygen is -1. The oxidation state of oxygen can range from -2 to +6, so -1 is also within this range. Thus, H2O2 can act as both an oxidizing and reducing agent.

4. **Conclusion**:
- From the analysis, we find that O2, SO2, and H2O2 can act as both oxidizing and reducing agents. HNO3 cannot act as a reducing agent.

### Final Answer:
The substances that can act as both oxidizing and reducing agents are O2, SO2, and H2O2.

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