Surface chemistry deals with the phenomenon that occurs at the surfaces or interfaces. The interface or surface is represented by separating the bulk phases by a hyphen or a slash. For example, the interface between a solid and a gas may be represented by solid-gas or solid/gas. Due to complete miscibility, there is no interface between the gases. The bulk phases that we come across in surface chemistry may be pure compounds or solutions. The interface is normally a few molecules thick but its area depends on the size of the particles of bulk phases. Many important phenomena, noticeable amongst these being corrosion, electrode processes, heterogeneous catalysis, dissolution and crystallization occur at interfaces. The subject of surface chemistry finds many applications in industry, analytical work and daily life situations.
Which statement is not correct for chemisorption?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → It is reversible
In chemisorption the adsorbate is held on the surface by chemical bonds (enthalpy of adsorption about 80–240 kJ mol−1), much like a surface compound. Such bonds are not broken just by lowering the pressure, so chemisorption is irreversible.
Option (1) It is highly specific — A property of chemisorption. It takes place only where the adsorbent and adsorbate can form chemical bonds.
Option (2) It is reversible — Not a property of chemisorption. The chemical bonds are not broken just by lowering the pressure, so chemisorption is irreversible; reversibility belongs to physisorption.
Option (3) It results in unimolecular layer — A property of chemisorption. Once every surface site is bonded, further molecules cannot bond to the surface, so chemisorption gives a single layer.
Option (4) It is favoured at high temperature — A property of chemisorption. It needs activation energy, so it increases with temperature (up to a point), unlike physisorption.
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 – …
