In Vander Waals equation of state of the gas law, the constant '$$b$$' is a measure of

Key Chemical Concept: van der Waals Constants

The van der Waals equation modifies the Ideal Gas Law to account for the behavior of real gases using two constants:

$$\left(P + \frac{an^2}{V^2}\right)(V - nb) = nRT$$

• Constant $$a$$: Measures the magnitude of the intermolecular attractive forces between gas molecules.
• Constant $$b$$: Represents the effective volume or co-volume occupied by the gas molecules themselves. It accounts for the fact that gas molecules are not mathematical point masses but hard spheres that take up a finite amount of physical space, thereby reducing the free volume available for motion.

Conclusion:

The constant $$b$$ serves as a direct correction factor for the finite volume occupied by the gas particles.

Answer: Option C — Volume occupied by the molecules