In van der Waal's equation of state of the gas law, constant 'a' and 'b' are used. The constant 'b' is a measure of

Options

A. Volume occupied by the molecules
B. Intermolecular attraction
C. Intermolecular repulsions
D. Intermolecular collisions per unit volume

Answer

To solve the question regarding the constant 'b' in van der Waals equation of state, we will follow these steps:

### Step 1: Write the van der Waals equation
The van der Waals equation is given by:

\[ \left(P + \frac{a n^2}{V^2}\right)(V - nB) = nRT \]

Where:
- \( P \) = pressure of the gas
- \( n \) = number of moles of the gas
- \( V \) = volume of the gas
- \( R \) = universal gas constant
- \( T \) = temperature
- \( a \) = van der Waals constant related to the attractive forces between molecules
- \( b \) = van der Waals constant related to the volume occupied by the gas molecules

### Step 2: Understand the meaning of constants 'a' and 'b'
- The constant \( a \) accounts for the attractive forces between gas molecules. It corrects the pressure of the gas due to these intermolecular forces.
- The constant \( b \) represents the volume occupied by the gas particles themselves. This is also referred to as the "excluded volume" because it accounts for the volume that is not available for molecular motion due to the presence of the gas molecules.

### Step 3: Identify what constant 'b' measures
From the above understanding, we can conclude that the constant \( b \) is a measure of the volume occupied by the gas molecules.

### Conclusion
Thus, the correct answer is that the constant 'b' in van der Waals equation is a measure of the volume occupied by gas particles.