Which one of the following is NOT applicable to the phenomenon of Adsorption?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → It is an endothermic process
Adsorption is always exothermic: the residual forces on the surface are partly satisfied and the surface energy falls.
Option (1) It is an endothermic process — Does not apply to adsorption. Adsorption releases heat (ΔH negative), so it is not endothermic.
Option (2) Entropy change is negative — Applies to adsorption. The gas molecules become restricted to the surface and lose freedom of movement.
Option (3) Gibb’s free energy change is less than zero — Applies to adsorption. Adsorption is spontaneous because ΔH is negative enough to make ΔG = ΔH − TΔS negative.
Option (4) Enthalpy of chemisorption is higher than that of physisorption — Applies to adsorption. Chemisorption involves chemical bonds (80–240 kJ mol−1), physisorption only van der Waals forces (20–40 kJ mol−1).
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):
Mechanism of Adsorption – …
