Which relationship does hold for Van der Waals gas under all conditions, where all terms have their usual meaning?

The van der Waals equation is an equation of state that corrects for two properties of real gases: the excluded volume of gas particles and attractive forces between gas molecules.The van der Waals equation is frequently presented as:$(P+\frac{a{n}^2}{V^2})(V-nb)=nRT$

The constant 'a' gives the idea of the magnitude of attractive forces between the molecules of the gas and 'b' is the measure of effective volume occupied by the gas molecules in the van der Waals equation. It is also called co-volume or excluded volume.