explain the physical significance of van der waals parameter? 

Dear user,

The van der Waals’ equation can be written as follows:

Significance of van der Waals’ parameter ‘a’:
It is the measure of the magnitude of attractive forces between the molecules of a gas.
Unit: atm L² mol⁻² or bar L² mol⁻²
Larger the value of ‘a’, larger will be the intermolecular force of attraction.
It is independent of pressure and temperature.

Significance of van der Waals’ parameter ‘b’:
It is the measure of the effective size of gas molecules.
Unit: L mol⁻¹

Hope, this answers your question.

Cheers!!