The accumulation of molecular species at the surface rather than in the bulk of a solid or liquid is termed as adsorption. There are two types of adsorption. In physisorption, attractive forces are mainly Van der Waals while in chemical adsorption adsorbate is held to the adsorbent by chemical bonds. Adsorption increases with increase in pressure and decreases as temperature is increased.
Critical temperature of few gases are given \(SO_2\) (630K), \(CH_4\) (190 K), \(H_2\) (33K). What is the correct order of ease of physi-adsorption of these gases?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \(SO_2 > CH_4 > H_2\)
Physisorption is held by van der Waals forces. Gases that liquefy easily have stronger van der Waals forces, and a gas liquefies more easily the higher its critical temperature. So the higher the critical temperature, the more readily the gas is physically adsorbed.
SO2 — Tc = 630 K: most easily adsorbed.
CH4 — Tc = 190 K.
H2 — Tc = 33 K: least adsorbed.
Shortcut: only Option (2) starts with \( \ce{SO2} \), the gas with the highest critical temperature.
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 – …
