One gas bleaches the colour of flowers by reduction, while the other by oxidation, the two gases respectively are:

Options

A. `CO and Cl_(2)`
B. `H_(2)S and Br_(2)`
C. `NH_(3) and SO_(3)`
D. `SO_(2) and Cl_(2)`

Explanation

To solve the question regarding the two gases that bleach the color of flowers by reduction and oxidation, we can break down the solution into clear steps:

### Step-by-Step Solution:

1. **Identify the Gases**:
- We need to identify two gases that have bleaching properties. One gas should act as a reducing agent, while the other acts as an oxidizing agent.

2. **Gas that Bleaches by Reduction**:
- The gas that bleaches by reduction is **Sulfur Dioxide (SO2)**.
- SO2 acts as a reducing agent because it can donate electrons to colored substances, effectively reducing them and removing their color.

3. **Mechanism of SO2 Bleaching**:
- When SO2 is dissolved in water, it forms sulfurous acid (H2SO3). This can further generate nascent hydrogen, which is a powerful reducing agent.
- The nascent hydrogen interacts with colored compounds (such as dyes), converting them into colorless compounds through reduction.

4. **Gas that Bleaches by Oxidation**:
- The gas that bleaches by oxidation is **Chlorine (Cl2)**.
- Cl2 acts as an oxidizing agent because it can accept electrons from colored substances, leading to the oxidation of these substances and the removal of their color.

5. **Mechanism of Cl2 Bleaching**:
- When Cl2 is dissolved in water, it forms hydrochloric acid (HCl) and nascent oxygen.
- The nascent oxygen interacts with colored compounds, oxidizing them and converting them into colorless compounds.

6. **Conclusion**:
- Therefore, the two gases that bleach the color of flowers by reduction and oxidation are:
- **SO2** (bleaches by reduction)
- **Cl2** (bleaches by oxidation)

### Final Answer:
The two gases respectively are **Sulfur Dioxide (SO2)** and **Chlorine (Cl2)**.

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