Rate of physisorption increases with:

The correct answer is Option (2) → Decrease in temperature

Physisorption is exothermic (adsorbate + adsorbent ⇌ adsorbate on surface + heat). By Le Chatelier’s principle, lowering the temperature shifts this equilibrium towards adsorption, so physical adsorption increases as the temperature decreases. It also increases with higher pressure and larger surface area.

Why the other options are incorrect

• Option (1) Increase in temperature — Incorrect. Since physisorption is exothermic, raising the temperature decreases it.

• Option (3) Decrease in pressure — Incorrect. Adsorption of a gas increases with increase in pressure; lowering the pressure causes desorption.

• Option (4) Decrease in surface area — Incorrect. A smaller surface area offers fewer sites, so less gas is adsorbed.

Note 1: 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):
Reversible Nature – “… Since the adsorption process is exothermic, the physical adsorption occurs readily at low temperature and decreases with increasing temperature (Le-Chatelier’s principle).”

Note 2: The same/similar question has been asked in different years by NTA as per the details given below: