The colloids that cannot be easily coagulated are
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Lyophilic colloids
In a lyophilic (solvent-loving) sol the particles are strongly solvated by the dispersion medium. This layer of solvent keeps the particles apart, so the sol is stable and is not easily coagulated; it is also reversible, because the dry residue goes back into the sol on adding the medium.
Why the other options are incorrect
Option (1) Lyophobic colloids — Incorrect. Are not solvated; they are coagulated readily by small amounts of electrolytes, by heating or by shaking.
Option (3) Irreversible sols — Incorrect. Another name for lyophobic sols, so they too coagulate easily.
Option (4) Associated colloids — Incorrect. Micelles exist only above the critical micelle concentration and break up on dilution; they are not the class described as hard to coagulate.
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):
Lyophilic Colloids
