Generally the major component of soap bars is :
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → \(CH_3(CH_2)_{16}COO^-Na^+\)
A soap is the salt of a fatty acid, so its polar head is a carboxylate group, –\( \ce{COO^{-}} \), joined to a long hydrophobic hydrocarbon tail. Option (3) is sodium stearate, the sodium salt of stearic acid (\( \ce{C17H35COOH} \)).
Why the other options are incorrect
Option (1) CH3(CH2)15N+(CH3)3Br− — Incorrect. This is cetyltrimethylammonium bromide, a cationic detergent (used in hair conditioners). Its head is a quaternary ammonium ion, not a carboxylate.
Option (2) CH3(CH2)11OSO3−Na+ — Incorrect. This is sodium lauryl sulphate, an anionic detergent. It is the sodium salt of a long chain alkyl hydrogensulphate, not of a fatty acid.
Option (4) CH3(CH2)11N+(CH3)3Br− — Incorrect. This is also a quaternary ammonium salt with a shorter (C12) chain, a cationic detergent, not a soap.
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):
Mechanism of Micelle Formation
