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.
Emulsions are type of colloids in which the physical state of dispersed phase and dispersion medium are respectively:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → liquid, liquid
Emulsions are liquid–liquid colloidal systems: finely divided droplets of one liquid are dispersed in another liquid with which it does not mix. Both the dispersed phase and the dispersion medium are liquids (for example, milk is liquid fat dispersed in water).
Why the other options are incorrect
Option (1) solid, liquid — Incorrect. A solid dispersed in a liquid is a sol (e.g. paints, cell fluids).
Option (3) liquid, solid — Incorrect. A liquid dispersed in a solid is a gel (e.g. cheese, butter, jellies).
Option (4) gas, liquid — Incorrect. A gas dispersed in a liquid is a foam (e.g. froth, whipped cream).
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):
Emulsions – “These are liquid-liquid colloidal systems, i.e., the dispersion of finely divided droplets in another liquid. If a mixture of two immiscible or partially miscible liquids is shaken, a coarse dispersion of one liquid in the other is obtained which is called emulsion. Generally, one of the two liquids is water. There are two types of emulsions. (i) Oil dispersed in water (O/W type) and (ii) Water dispersed in oil (W/O type).”