Select the incorrect statement(s)
A. Surface active agents like soaps and synthetic detergents form micelles in water.
B. Soaps are emulsifying agents
C. \(C_{17}H_{35}\) (hydrocarbon) and \(-COO^-\) (carboxylate) part of stearate ion \(C_{17}H_{35}COO^-\) both are hydrophobic
D. Surfactants are basic in nature
Choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → C and D only
A soap or detergent ion has a long hydrophobic hydrocarbon tail and a hydrophilic ionic head. In water these ions gather into micelles, with the tails inside and the heads facing the water; oil and grease are held inside the micelles, which is how soaps emulsify and clean.
(A) Surface active agents like soaps and synthetic detergents form micelles in water — Correct. Above the critical micelle concentration their ions aggregate into micelles (associated colloids).
(B) Soaps are emulsifying agents — Correct. Soap stabilises oil-in-water emulsions; this is how it removes grease.
(C) C17H35 (hydrocarbon) and −COO− (carboxylate) part of stearate ion C17H35COO− both are hydrophobic — Incorrect. The \( \ce{C17H35} \) chain (tail) is hydrophobic, but the carboxylate group \( \ce{COO-} \) (head) is hydrophilic.
(D) Surfactants are basic in nature — Incorrect. This is not true of surfactants in general. Surfactants may be anionic (soaps), cationic (quaternary ammonium salts) or non-ionic (polyethylene glycol esters); only the solutions of soaps, salts of a weak acid and a strong base, are basic.
Note 1: 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):
Mechanism of Micelle Formation – “Let us take the example of soap solutions. Soap is sodium or potassium salt of a higher fatty acid and may be represented as RCOO–Na+ (e.g., sodium stearate CH3(CH2)16COO–Na+, which is a major component of many bar soaps). When dissolved in water, it dissociates into RCOO– and Na+ ions. The RCOO– ions, however, consist of two parts — a long hydrocarbon chain R (also called non-polar ‘tail’) which is hydrophobic (water repelling), and a polar group COO– (also called polar-ionic ‘head’), which is hydrophilic (water loving).”
Note 2: The same/similar question has been asked in different years by NTA as per the details given below:
| 2026 | 2025 | 2024 | 2023 | 2022 |
|---|---|---|---|---|
| – | – | – | 02-06 S3 31-05 S1 | – |