Which among the following compounds is used to identify the presence of water vapour in the atmosphere?

Options

A. Carbon dioxide
B. Phosphorus
C. Lime water
D. Anhydrous copper sulphate

Explanation

To solve the question "Which among the following compounds is used to identify the presence of water vapour in the atmosphere?", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: We need to identify a compound that can indicate the presence of water vapour in the atmosphere from the given options.

2. **Review the Options**:
- Option 1: Carbon Dioxide
- Option 2: Phosphorus
- Option 3: Lime Water
- Option 4: Anhydrous Copper Sulphate

3. **Analyze Each Option**:
- **Carbon Dioxide**: This gas does not indicate the presence of water vapour.
- **Phosphorus**: Phosphorus is not used for detecting water vapour.
- **Lime Water**: Lime water is used to test for carbon dioxide, not water vapour.
- **Anhydrous Copper Sulphate**: This compound is known for its ability to absorb water. When it comes into contact with water vapour, it changes from white to blue, indicating the presence of water.

4. **Identify the Correct Compound**: The only compound among the options that changes color in the presence of water vapour is **Anhydrous Copper Sulphate** (CuSO4). When it absorbs water, it forms hydrated copper sulphate (CuSO4·5H2O), which is blue in color.

5. **Conclusion**: Therefore, the correct answer is **Option 4: Anhydrous Copper Sulphate**.