Which of the following statements is not applicable to chemisorption?…

The correct answer is Option (4) → A only

Chemisorption is adsorption by chemical bond formation between the adsorbate and the adsorbent. It has a high activation energy, so it is slow at low temperature and increases as the temperature rises.

• A. It is independent of temperature. — Not applicable to chemisorption. Like most chemical changes, chemisorption increases with rise of temperature (up to a point), because of its high activation energy.

• B. It is highly specific — Applicable to chemisorption. It occurs only when the adsorbate can form a chemical bond with the adsorbent (\( \ce{O2} \) on metals as oxides, \( \ce{H2} \) on transition metals as hydrides).

• C. It is slow — Applicable to chemisorption. The high energy of activation makes it slow, especially at low temperatures.

• D. It is irreversible — Applicable to chemisorption. It involves compound formation, so it is usually irreversible.

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):
Characteristics of Chemisorption – “(i) High specificity: Chemisorption is highly specific and it will only occur if there is some possibility of chemical bonding between adsorbent and adsorbate. For example, oxygen is adsorbed on metals by virtue of oxide formation and hydrogen is adsorbed by transition metals due to hydride formation.
(ii) Irreversibility: As chemisorption involves compound formation, it is usually irreversible in nature. Chemisorption is also an exothermic process but the process is very slow at low temperatures on account of high energy of activation. Like most chemical changes, adsorption often increases with rise of temperature.”