In van der Waals' equation of state of the gas law the constnat 'b' is a measure of .

Options

A. intermolecular attraction
B. intermolecular repulsions
C. intermolecular collision per unit volume
D. volume occupied by the molecules

Answer

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

### Step 1: Understand the van der Waals equation
The van der Waals equation is an adjustment of the ideal gas law that accounts for the volume occupied by gas molecules and the intermolecular forces. It is expressed as:
\[ (P + a(n/V)^2)(V - nb) = nRT \]
where:
- \( P \) = pressure,
- \( V \) = volume,
- \( n \) = number of moles,
- \( R \) = universal gas constant,
- \( T \) = temperature,
- \( a \) = measure of the attraction between molecules,
- \( b \) = volume occupied by the gas molecules.

### Step 2: Identify the role of the constant 'b'
In the van der Waals equation, the constant 'b' represents the volume occupied by the gas molecules themselves. This means that it accounts for the finite size of the molecules, which is not considered in the ideal gas law.

### Step 3: Analyze the options
The options provided in the question are:
1. Intermolecular attraction
2. Intermolecular repulsion
3. Intermolecular collision per unit volume
4. Volume occupied by molecules

From our understanding, the correct interpretation of 'b' aligns with option 4, as it specifically refers to the volume occupied by the molecules.

### Step 4: Conclusion
Thus, the constant 'b' in the van der Waals equation is a measure of the volume occupied by the gas molecules.

### Final Answer:
The correct answer is: **Volume occupied by molecules (Option D)**.

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