Out of the four liquids given below, the one having lowest vapour pressure at `25^(@)C` is

Options

A. Carbon tetrachloride
B. Benzene
C. Chloroform
D. Water

Explanation

To determine which of the four liquids has the lowest vapor pressure at 25°C, we need to understand the concept of vapor pressure and the factors that influence it.

### Step-by-Step Solution:

1. **Understand Vapor Pressure**:
- Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid at a given temperature. It reflects the tendency of the liquid to evaporate. A higher vapor pressure indicates a greater tendency to evaporate.

2. **Identify the Liquids**:
- The four liquids given are:
- A) Carbon Tetrachloride (CCl₄)
- B) Benzene (C₆H₆)
- C) Chloroform (CHCl₃)
- D) Water (H₂O)

3. **Analyze Intermolecular Forces**:
- The vapor pressure of a liquid is influenced by the strength of its intermolecular forces. Stronger intermolecular forces result in lower vapor pressure because the molecules are held more tightly together.
- Water exhibits strong hydrogen bonding due to the presence of hydrogen atoms bonded to highly electronegative oxygen atoms. This results in significant intermolecular attraction.

4. **Compare the Intermolecular Forces**:
- **Water (H₂O)**: Strong hydrogen bonding.
- **Carbon Tetrachloride (CCl₄)**: Dispersion forces (weak).
- **Benzene (C₆H₆)**: Dispersion forces (weak).
- **Chloroform (CHCl₃)**: Dipole-dipole interactions, but weaker than hydrogen bonding.

5. **Conclusion**:
- Since water has the strongest intermolecular forces (hydrogen bonding), it will have the lowest vapor pressure among the four liquids at 25°C. The other three liquids (CCl₄, C₆H₆, CHCl₃) have weaker intermolecular forces, leading to higher vapor pressures.

### Final Answer:
The liquid with the lowest vapor pressure at 25°C is **Water (H₂O)**.

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