Bleaching action of `SO_2` is due to______.

Answer

To determine the bleaching action of sulfur dioxide (SO₂), we need to analyze its chemical properties and how it interacts with colored materials.

### Step-by-Step Solution:

1. **Understanding Bleaching Action**: Bleaching refers to the process of removing color from a material. This can be achieved through various chemical reactions that either reduce the colored compounds or oxidize them.

2. **Properties of SO₂**: Sulfur dioxide is known for its reducing properties. A reducing agent is a substance that donates electrons to another substance, causing the other substance to be reduced.

3. **Reaction with Water**: When SO₂ is treated with water, it can form sulfurous acid (H₂SO₃). In this process, nascent hydrogen (which is hydrogen in its atomic form) is generated, which plays a crucial role in the reduction process.

4. **Reduction Process**: The nascent hydrogen interacts with the colored materials, reducing them to colorless compounds. This is the essence of the bleaching action of SO₂. The colored material loses its color due to the reduction reaction.

5. **Temporary Nature of Bleaching**: It is important to note that the bleaching action of SO₂ is temporary. If the bleached material is exposed to oxygen again, it can be oxidized back to its colored form. This is because the reduction process is reversible under certain conditions.

6. **Comparison with Other Bleaching Agents**: For contrast, chlorine (Cl₂) acts as a bleaching agent through oxidation, which is a permanent process. When chlorine reacts with water, it forms hydrochloric acid (HCl) and nascent oxygen, which permanently bleaches the material.

### Conclusion:
The bleaching action of SO₂ is due to its **reducing property**.