Which of the following is the correct range of critical micelle concentrations (CMC) for soaps?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → \(10^{-4}\) to \(10^{-3}\) mol/L
Soaps are associated colloids: at low concentration they behave as normal electrolytes, but above a particular temperature (Kraft temperature) and above a particular concentration they aggregate into micelles. That concentration is the critical micelle concentration (CMC). For soaps, the CMC is 10−4 to 10−3 mol L−1.
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 (Tk) and above a particular concentration called critical micelle concentration (CMC). On dilution, these colloids revert back to individual ions. Surface active agents such as soaps and synthetic detergents belong to this class. For soaps, the CMC is 10−4 to 10−3 mol L−1.”