Which of the following statements is incorrect regarding physissorptions?

Physisorption (physical adsorption) is governed by weak van der Waals interactions between the adsorbate molecules and the solid surface. Let us analyse each statement one by one.

Case A: “It occurs because of van der Waals forces.”
Physisorption is indeed caused by instantaneous dipole-induced dipole attractions, London dispersion forces, etc., which are collectively called van der Waals forces. Hence, Statement A is correct.

Case B: “More easily liquefiable gases are adsorbed readily.”
The ease of liquefaction is directly related to the magnitude of van der Waals forces present in the gas. Gases with higher polarizability (easily liquefiable) interact more strongly with the adsorbent surface and therefore get adsorbed to a greater extent. Hence, Statement B is correct.

Case C: “Under high pressure it results into multimolecular layer on adsorbent surface.”
Because the interaction between molecules and surface is weak, additional layers of gas molecules can build up upon the first layer when pressure is increased. This leads to formation of multilayers typical of physisorption. Hence, Statement C is correct.

Case D: “Enthalpy of adsorption ($$\Delta H_{\text{adsorption}}$$) is low and positive.”
Although the magnitude of enthalpy of physisorption is indeed low (about $$20-40\ \text{kJ mol}^{-1}$$), adsorption is an exothermic process; heat is released when molecules adhere to the surface. Therefore $$\Delta H_{\text{adsorption}}$$ is low but negative, not positive. Hence, Statement D is incorrect.

Therefore, the statement that does not hold true for physisorption is:
Option D which is: Enthalpy of adsorption ($$\Delta H_{\text{adsorption}}$$) is low and positive.