Chlorine acts as a bleaching agent only in the presence of

Options

A. Dry air
B. Moisture
C. Sunlight
D. Pure oxygen

Explanation

To solve the question regarding the conditions under which chlorine acts as a bleaching agent, we can follow these steps:

### Step 1: Understand the Role of Chlorine
Chlorine (Cl₂) is known for its bleaching properties, which means it can remove color from substances. However, it does not act as a bleaching agent under all conditions.

### Step 2: Identify the Required Conditions
From the information provided, chlorine acts as a bleaching agent in the presence of:
- Dry ether
- Moisture
- Sunlight
- Pure oxygen

### Step 3: Focus on Moisture
Among these conditions, moisture (water) is particularly important. When chlorine comes into contact with water, it undergoes a chemical reaction.

### Step 4: Chemical Reaction with Water
In the presence of moisture, chlorine reacts with water to form hydrochloric acid (HCl) and hypochlorous acid (HClO):
\[ \text{Cl}_2 + \text{H}_2\text{O} \rightarrow \text{HCl} + \text{HClO} \]

### Step 5: Formation of Nascent Oxygen
Hypochlorous acid (HClO) is unstable and can dissociate to release nascent oxygen (O):
\[ \text{HClO} \rightarrow \text{HCl} + \text{O} \]

### Step 6: Bleaching Action
This nascent oxygen is the active bleaching agent. When colored materials come into contact with nascent oxygen, they lose their color and become colorless.

### Conclusion
Thus, chlorine acts as a bleaching agent only in the presence of moisture. Therefore, the correct answer to the question is:
**Moisture (Option B)**.

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