Which of the following is not the characteristic of physisorption?

The correct answer is Option (3) → Enthalpy of adsorption is high

In physisorption the gas is held on the surface of the adsorbent by weak van der Waals forces, not by chemical bonds. Because these forces are weak, the enthalpy of physisorption is low, about 20–40 kJ mol⁻¹. A high enthalpy of adsorption (80–240 kJ mol⁻¹) belongs to chemisorption, where chemical bonds are formed.

• Option (1) It arises because of van der Waals forces — A characteristic of physisorption. The weak van der Waals attraction is what makes it physical adsorption.

• Option (2) It is not specific in nature — A characteristic of physisorption. Any gas is adsorbed on the surface of any solid to some extent.

• Option (3) Enthalpy of adsorption is high — Not a characteristic of physisorption. Weak forces release little heat, so the enthalpy of physisorption is low; a high enthalpy is typical of chemisorption.

• Option (4) It results in multimolecular layers on the adsorbent surface under high pressure. — A characteristic of physisorption. Unlike chemisorption, which gives a single layer, physisorption builds up several layers at high pressure.

Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.

NCERT (Pre-rationalised edition, 2022-23):
Types of Adsorption – …