When `SO_2` is passed through aqueous `H_2 S` sulphur is precipitated. In this reaction, `SO_2` acts as

Options

A. an oxidising agent
B. a reducing agent
C. an acld
D. a complexing agent

Explanation

To determine the role of \( SO_2 \) when it is passed through aqueous \( H_2S \) and precipitates sulfur, we can analyze the chemical reaction involved.

### Step-by-Step Solution:

1. **Identify the Reactants and Products**:
- The reactants are \( SO_2 \) (sulfur dioxide) and \( H_2S \) (hydrogen sulfide).
- The product formed is elemental sulfur (\( S \)).

2. **Understand the Reaction**:
- When \( SO_2 \) is introduced to \( H_2S \), a redox reaction occurs. In this reaction, \( H_2S \) is oxidized, and \( SO_2 \) is reduced.

3. **Determine Oxidation and Reduction**:
- **Oxidation**: The process where a substance loses electrons. In this case, \( H_2S \) loses electrons and is oxidized to form sulfur.
- **Reduction**: The process where a substance gains electrons. Here, \( SO_2 \) gains electrons and is reduced to form elemental sulfur.

4. **Identify the Role of \( SO_2 \)**:
- Since \( SO_2 \) gains electrons during the reaction, it acts as an oxidizing agent. An oxidizing agent is a substance that facilitates the oxidation of another substance while being reduced itself.

5. **Conclusion**:
- Therefore, in the reaction where \( SO_2 \) is passed through aqueous \( H_2S \) and precipitates sulfur, \( SO_2 \) acts as an **oxidizing agent**.

### Final Answer:
**SO₂ acts as an oxidizing agent.**

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