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.
For colloids, the experiment of electrophoresis proves
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → charge on colloidal particle
Only charged particles move in an electric field. In electrophoresis the sol particles move to one electrode, so the experiment confirms the charge on colloidal particles and shows its sign.
Why the other options are incorrect
Option (1) size of the colloidal particle — Incorrect. Electrophoresis does not measure particle size; size is studied by methods such as the ultramicroscope.
Option (2) homogeneous mixture — Incorrect. A sol is heterogeneous (two phases); electrophoresis has nothing to do with proving homogeneity.
Option (4) Tyndall effect — Incorrect. That is the scattering of light by colloidal particles, a separate optical property, not an electrical one.
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):
Electrophoresis
