Bleaching of flowers by chlorine is permanet, while that by sulphur dioxide is temporary. Explain.

Answer

To explain why the bleaching of flowers by chlorine is permanent while that by sulfur dioxide is temporary, we can break down the processes involved in each case.

### Step 1: Bleaching by Chlorine
1. **Chemical Reaction**: When chlorine gas (Cl₂) is used for bleaching, it reacts with water (H₂O) to produce hydrochloric acid (HCl) and nascent oxygen (O).
\[ \text{Cl}_2 + \text{H}_2\text{O} \rightarrow \text{HCl} + \text{O} \text{ (nascent)} \]

2. **Mechanism of Bleaching**: The nascent oxygen produced in this reaction acts as a strong oxidizing agent. It oxidizes the colored compounds in the flowers, breaking down their structure and converting them into colorless compounds.

3. **Permanence of Bleaching**: Since the oxidation process changes the chemical structure of the colored materials irreversibly, the bleaching effect is permanent. Once the color is removed through oxidation, it cannot be restored.

### Step 2: Bleaching by Sulfur Dioxide
1. **Chemical Reaction**: When sulfur dioxide (SO₂) is used for bleaching, it reacts with water to form sulfuric acid (H₂SO₄) and nascent hydrogen (H).
\[ \text{SO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{SO}_4 + \text{H} \text{ (nascent)} \]

2. **Mechanism of Bleaching**: The nascent hydrogen acts as a reducing agent, which reduces the colored compounds to colorless forms.

3. **Temporary Nature of Bleaching**: The reduction process is reversible. If the flowers are exposed to air (which contains oxygen), the nascent hydrogen can react with oxygen, allowing the colored compounds to regain their color. This means that the bleaching effect is temporary.

### Conclusion
- **Chlorine Bleaching**: Permanent due to oxidation.
- **Sulfur Dioxide Bleaching**: Temporary due to reduction, which can be reversed by exposure to air.