A colloid is a heterogeneous system in which one substance is dispersed as very fine particles in another substance called dispersion medium. Colloids are classified on the basis of physical state of dispersed phase and dispersion medium, nature of interaction between dispersed phase and dispersion medium and types of particles of dispersed phase. There are various methods for the preparation of colloidal solutions such as chemical methods, electrical disintegration and peptization. Colloidal solutions when prepared, generally contain excessive amount of electrolytes, and some other soluble impurities. The process used for reducing the amount of impurities to a requisite minimum is known as purification of colloidal solution. Purification of colloidal solution is carried out by various methods such as Dialysis, Electrodialysis, Ultrafiltration etc. Colligative properties, Tyndall effect, colour, Brownian movement, charge on colloidal particles, electrophoresis, coagulation are various properties exhibited by colloidal solution.
The formation of micelles takes place only above a particular temperature known as:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Kraft temperature
Soaps and detergents are associated colloids: at low concentration they behave as normal strong electrolytes, but at higher concentration their ions aggregate into micelles, with the hydrocarbon tails inside and the polar heads outside. Micelles form only above a particular temperature, the Kraft temperature (Tk), and above a particular concentration, the critical micelle concentration (CMC).
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):
Classification Based on Type of Particles of the Dispersed Phase, Multimolecular, Macromolecular and Associated Colloids – “… (iii) Associated colloids (Micelles): There are some substances which at low concentrations behave as normal strong electrolytes, but at higher concentrations exhibit colloidal behaviour due to formation of aggregates. The aggregated particles thus formed are called micelles. These are also known as associated colloids. The formation of micelles takes place only above a particular temperature called Kraft temperature (Tk) and above a particular concentration called critical micelle concentration (CMC).”