Which of the following processes do not occur at the interface of pha…

The correct answer is Option (3) → Homogeneous Catalysis

An interface is the boundary between two bulk phases (solid/gas, solid/liquid, liquid/liquid). Surface chemistry deals with processes that take place at such boundaries. In homogeneous catalysis the reactants and the catalyst are in the same phase, so there is no phase boundary, for example:

    \( \displaystyle \ce{2SO2(g) + O2(g)} \xrightarrow{\ce{NO(g)}} \ce{2SO3(g)} \)

• Option (1) Crystallization — Occurs at an interface. Crystals grow at the solid/solution interface.

• Option (2) Heterogeneous Catalysis — Occurs at an interface. The reactants are adsorbed and react on the surface of a catalyst in another phase, for example \( \ce{N2} \) and \( \ce{H2} \) on solid iron.

• Option (3) Homogeneous Catalysis — Does not occur at an interface. Reactants and catalyst are in one phase, so there is no boundary between phases.

• Option (4) Corrosion — Occurs at an interface. It takes place at the metal/air or metal/water interface.

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 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 crystallisation occur at interfaces.”