When an article is bleached by `SO_(2)` it loses its colour. The colour can be restored by :

Options

A. exposure to air
B. heating
C. dilution
D. none of these

Explanation

To solve the problem of restoring color to an article that has been bleached by sulfur dioxide (SO₂), we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Bleaching Process**:
- When an article is bleached with SO₂, it loses its color due to a reduction reaction. SO₂ reacts with water (H₂O) to form sulfuric acid (H₂SO₄) and hydrogen ions (H⁺).
- The presence of H⁺ ions leads to the decolorization of the dye or colored article.

2. **Identifying the Nature of Bleaching**:
- The bleaching caused by SO₂ is temporary. This means that the color can potentially be restored after the bleaching process.

3. **Restoration of Color**:
- To restore the color of the bleached article, we need to reverse the reduction process. This can be achieved by oxidation.
- When the article is exposed to air, it comes into contact with oxygen (O₂) present in the atmosphere.

4. **Oxidation Reaction**:
- The excess oxygen in the air can react with the colorless matter (which was previously colored) and oxidize it back to its original colored state.
- The reaction can be represented as:
\[ 2H^+ + \frac{1}{2} O_2 \rightarrow H_2O \]
- This indicates that the addition of oxygen restores the color by converting the reduced form back to its oxidized form.

5. **Evaluating the Options**:
- Now, let's evaluate the options provided:
1. Exposure to air (correct, as it provides oxygen for oxidation).
2. On heating (not relevant to restoring color).
3. Dilution (does not contribute to restoring color).
4. None of these (incorrect since exposure to air is a valid option).

6. **Conclusion**:
- The correct answer is **exposure to air**, as it allows for the oxidation of the colorless article, restoring its original color.

### Final Answer:
The color can be restored by **exposure to air**.

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