Identify the incorrect statement among the following?

Options

A. Van der Waal's constant 'a' is a measure of intermolecular force of attraction between the molecules.
B. Intermolecular force of attraction increases with the increase in pressure
C. Van der Waal's constant 'a' becomes negligible at high pressure.
D. None of these

Answer

To solve the question of identifying the incorrect statement among the given options, we will analyze each statement one by one based on our understanding of the Van der Waals equation and the behavior of gases.

### Step-by-Step Solution:

1. **Understanding the Van der Waals Equation**:
The Van der Waals equation is given by:
\[ \left( p + \frac{a n^2}{V^2} \right) (V - nb) = nRT \]
Here, \( p \) is the pressure, \( V \) is the volume, \( n \) is the number of moles, \( R \) is the universal gas constant, \( T \) is the temperature, \( a \) is the Van der Waals constant related to intermolecular forces, and \( b \) is the volume occupied by the gas molecules.

2. **Analyzing Statement 1**:
- **Statement**: "Van der Waals constant A measures intermolecular forces of attraction between the molecules."
- **Analysis**: This statement is correct. The constant \( a \) in the Van der Waals equation accounts for the attractive forces between gas molecules.

3. **Analyzing Statement 2**:
- **Statement**: "Intermolecular forces increase with increase in pressure."
- **Analysis**: This statement is also correct. As pressure increases, gas molecules are forced closer together, which enhances the intermolecular forces between them.

4. **Analyzing Statement 3**:
- **Statement**: "Van der Waals constant A becomes negligible at high pressure."
- **Analysis**: This statement is misleading. While the pressure correction term \( \frac{a n^2}{V^2} \) may become negligible at very high pressures, the constant \( a \) itself does not become negligible; rather, its effect in the equation diminishes under certain conditions. Thus, this statement is incorrect.

5. **Analyzing Statement 4**:
- **Statement**: "None of these."
- **Analysis**: Since we have identified that statement 3 is incorrect, this option cannot be correct.

### Conclusion:
The incorrect statement among the options is:
- **"Van der Waals constant A becomes negligible at high pressure."**

### Final Answer:
The answer is option 3.