The process of accumulation of molecular species at the surface of solid or liquid is called adsorption. It may be physisorption or chemisorption. Low temperature is favourable for physisorption. Amount of gas adsorbed by a solid depends upon nature of gas. Easily liquefiable gases are readily adsorbed. Catalyst increases the rate of reaction. Catalysis may be homogeneous or heterogeneous. Enzymes are biological catalysts. They work at optimum pH and temperature. Solutions are of three types i.e. true solutions, colloids and suspensions. Depending on the interaction between dispersed phase and dispersion medium colloids may be Lyophilic and Lyophobic. Depending on type of particles there may be multimolecular, macro-molecular and associated colloids. Sol, gel, emulsions are also various types of colloids.
The correct order of rate of adsorption of different gases by 1g activated charcoal is:
A. \(H_2 < CH_4 < SO_2\)
B. \(H_2 < SO_2 < CH_4\)
C. \(CH_4 < SO_2 < H_2\)
D. \(SO_2 < CH_4 < H_2\)
E. \(SO_2 < H_2 < CH_4\)
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A only
The amount of gas adsorbed by a solid depends on the nature of the gas. Easily liquefiable gases, that is, gases with higher critical temperatures, are adsorbed more readily, because van der Waals forces are stronger near the critical temperature.
The order asked is the extent (amount) of adsorption per gram of charcoal, which is set by the critical temperatures: \( \ce{H2} \) (33 K) < \( \ce{CH4} \) (190 K) < \( \ce{SO2} \) (630 K).
(A) \(H_2 < CH_4 < SO_2\) — Correct. This follows the critical temperatures.
(B) \(H_2 < SO_2 < CH_4\) — Incorrect. \( \ce{SO2} \) (630 K) is adsorbed more than \( \ce{CH4} \) (190 K).
(C) \(CH_4 < SO_2 < H_2\) — Incorrect. \( \ce{H2} \), with the lowest critical temperature, is adsorbed least, not most.
(D) \(SO_2 < CH_4 < H_2\) — Incorrect. This is the reverse of the correct order.
(E) \(SO_2 < H_2 < CH_4\) — Incorrect. \( \ce{SO2} \) is adsorbed most and \( \ce{H2} \) least.
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):
Nature of Adsorbate
