Vapour pressure is the pressure exerted by vapours

Options

A. In equilibrium with liquid
B. In any condition
C. In an open system
D. In atmospheric conditions

Answer

### Step-by-Step Solution:

1. **Understanding Vapor Pressure**:
- Vapor pressure is defined as the pressure exerted by the vapor of a substance when it is in equilibrium with its solid or liquid phase. This means that the rate of evaporation of the liquid equals the rate of condensation of the vapor.

2. **Equilibrium Condition**:
- For vapor pressure to be measured, the system must be in a closed container. This ensures that the vapor does not escape and that the pressure can build up until equilibrium is reached.

3. **Temperature Dependence**:
- Vapor pressure is dependent on temperature. At a given temperature, each substance has a specific vapor pressure which can change with temperature variations.

4. **Correct Statement**:
- The correct completion of the statement is: "Vapor pressure is the pressure exerted by vapors in equilibrium with a liquid or solid in a closed container at a given temperature."

5. **Evaluating Options**:
- If options are provided, we can evaluate them based on the definition:
- **In equilibrium with liquid**: Correct
- **In any condition**: Incorrect
- **In an open system**: Incorrect
- **In atmospheric conditions**: Incorrect

6. **Conclusion**:
- The most appropriate option that completes the statement correctly is the one that specifies equilibrium with a liquid in a closed container.