Which of the following behaves as both oxidising and reducing agents ?

Options

A. `H_2SO_4`
B. `SO_2`
C. `H_2S`
D. `HNO_3`

Explanation

To determine which of the following behaves as both an oxidizing and reducing agent, we need to analyze the oxidation states of the compounds given, specifically focusing on sulfur dioxide (SO2).

### Step-by-Step Solution:

1. **Understand the Definitions**:
- An **oxidizing agent** is a substance that gains electrons and is reduced in the process, leading to a decrease in its oxidation state.
- A **reducing agent** is a substance that loses electrons and is oxidized, leading to an increase in its oxidation state.

2. **Identify the Compound**:
- We will analyze sulfur dioxide (SO2) to see if it can act as both an oxidizing and reducing agent.

3. **Determine the Oxidation State of Sulfur in SO2**:
- The oxidation state of sulfur (S) in SO2 can be calculated as follows:
- Let the oxidation state of sulfur be \( x \).
- The formula for SO2 is: \( x + 2(-2) = 0 \) (since oxygen has an oxidation state of -2).
- This simplifies to: \( x - 4 = 0 \) ⇒ \( x = +4 \).
- Therefore, the oxidation state of sulfur in SO2 is +4.

4. **Evaluate the Possible Changes in Oxidation State**:
- **As an Oxidizing Agent**:
- SO2 can be oxidized to form sulfur trioxide (SO3), where sulfur has an oxidation state of +6.
- This means SO2 can increase its oxidation state from +4 to +6, thus acting as an oxidizing agent.
- **As a Reducing Agent**:
- SO2 can also be reduced to form hydrogen sulfide (H2S), where sulfur has an oxidation state of -2.
- This means SO2 can decrease its oxidation state from +4 to -2, thus acting as a reducing agent.

5. **Conclusion**:
- Since SO2 can both increase its oxidation state (acting as an oxidizing agent) and decrease its oxidation state (acting as a reducing agent), it behaves as both an oxidizing and reducing agent.

### Final Answer:
SO2 (sulfur dioxide) behaves as both an oxidizing and reducing agent.

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