The formation of micelle takes place only:
(A) above a particular temperature called Kraft temperature
(B) above a particular concentration called critical micelle concentration
(C) when catalyst is added
Choose the correct answer from the options given below :
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (A), (B) Only
Soaps and detergents are associated colloids: at low concentration they behave as ordinary electrolytes, and their ions aggregate into micelles only under two conditions.
(A) above the Kraft temperature — True. Micelles form only above a particular temperature called the Kraft temperature (Tk).
(B) above the critical micelle concentration — True. Micelles form only above a particular concentration, the CMC (about 10−4 to 10−3 mol L−1 for soaps); on dilution they break up into ions again.
(C) when catalyst is added — False. Micelle formation is a physical aggregation of ions; no catalyst is involved.
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):
Associated Colloids (Micelles) – “… The formation of micelles takes place only above a particular temperature called Kraft temperature and above a particular concentration called critical micelle concentration (CMC). On dilution, these colloids revert back to individual ions.”