Answer the questions based on the passage given below:
Adsorption is a surface phenomenon and it differs from absorption which occurs throughout the body of the substance that absorbs. In physisorption the attractive forces are mainly van der Waals forces while in chemisorption ionic / covalent bonds are formed between particles of adsorbent and adsorbate. The catalytic activity of finely divided iron in Haber's process of ammonia manufacture can be explained by adsorption theory. Adsorption being an exothermic process, the heat of adsorption is utilized in enhancing the rate of the reaction. Adsorption has many applications being used in gas masks, control of humidity, chromatograph separation, curing diseases etc.
Which of the following is not a surface phenomenon?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Fusion of solids
A surface phenomenon is one that takes place at the interface (boundary) between two phases.
Option (1) Fusion of solids — Not a surface phenomenon. Melting is a change of state of the whole solid: the lattice breaks down throughout the bulk at the melting point.
Option (2) Heterogeneous catalysis — A surface phenomenon. The reaction takes place on the surface of the solid catalyst after the reactants are adsorbed on it.
Option (3) Corrosion — A surface phenomenon. The metal is attacked at its surface, where it meets air and moisture.
Option (4) Electrolytic process — A surface phenomenon. Oxidation and reduction take place at the electrode surfaces, the interface between electrode and electrolyte.
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):
Surface Chemistry – “… Surface chemistry deals with phenomena that occur at the surfaces or interfaces. … 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 crystallisation occur at interfaces.”