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

To solve the question regarding vapor pressure, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition of Vapor Pressure**:
- Vapor pressure is defined as the pressure exerted by the vapor of a substance when it is in equilibrium with its liquid (or solid) form in a closed container at a specific temperature.

2. **Analyze the Given Options**:
- We have four options to consider:
- A) In equilibrium with liquid
- B) In any condition
- C) In an open system
- D) In atmospheric conditions

3. **Evaluate Each Option**:
- **Option A: In equilibrium with liquid**:
- This aligns with the definition of vapor pressure, as it specifically mentions equilibrium with liquid. This option is likely correct.
- **Option B: In any condition**:
- This is incorrect because vapor pressure is not defined for just any condition; it must be in a specific state of equilibrium.
- **Option C: In an open system**:
- This is also incorrect. Vapor pressure is measured in a closed container, not in an open system.
- **Option D: In atmospheric conditions**:
- This is misleading. While vapor pressure can be measured at atmospheric conditions, the definition requires a closed system for accurate measurement.

4. **Conclusion**:
- Based on the evaluation, the correct answer is **Option A: In equilibrium with liquid**.

### Final Answer:
Vapor pressure is the pressure exerted by vapors **in equilibrium with liquid**.

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