A colloid is a heterogeneous system in which one substance is dispersed as very fine particles in another substance. Their range of diameters is between 1-1000 nm. Based on dispersed phase and dispersion medium, colloids may be of different types like sol, gel, emulsion, aerosol, foam etc. Based on nature of interaction between two phases, sols are divided into Lyophilic and Lyophobic sols. Colloidal solutions exhibit various properties like Tyndall effect, Brownian movement and Electrophoresis. Stability of colloids is due to presence of charge. If somehow charge is removed, the particles will coagulate. Coagulation rate by various solutions containing ions, is decided by Hardy-Schulze rule. Everyday we come across many colloids. The meals we eat, clothes we wear, wooden furniture etc. are largely composed of colloids.
The process of movement of dispersion medium under the effect of electric field is known as
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Electroosmosis
When the colloidal particles are held back and cannot move in an electric field, the dispersion medium moves instead; this is electroosmosis. (Movement of the particles themselves is electrophoresis.)
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 – “The existence of charge on colloidal particles is confirmed by electrophoresis experiment. When electric potential is applied across two platinum electrodes dipping in a colloidal solution, the colloidal particles move towards one or the other electrode. The movement of colloidal particles under an applied electric potential is called electrophoresis. Positively charged particles move towards the cathode while negatively charged particles move towards the anode.”
Electrophoresis – “… When electrophoresis, i.e., movement of particles is prevented by some suitable means, it is observed that the dispersion medium begins to move in an electric field. This phenomenon is termed electroosmosis.”