Which one of the following is NOT a synthetic detergent?

Synthetic detergents are classified into anionic, cationic, and non-ionic types. Option 1 represents an anionic detergent (sodium alkyl sulfate), while Option 2 is a cationic detergent (quaternary ammonium salt) [1]. Option 4 is a non-ionic detergent, typically formed by the reaction of stearic acid with polyethylene glycol [1]. In contrast, Option 3, CH3(CH2)16COO-Na+ (sodium stearate), is a soap. Soaps are defined as sodium or potassium salts of long-chain carboxylic acids (fatty acids) [2]. While both soaps and synthetic detergents have hydrophobic and hydrophilic groups to emulsify dirt, soaps are produced via saponification of fats [2]. Unlike synthetic detergents, soaps form insoluble precipitates with calcium and magnesium ions in hard water, making them less effective cleansing agents in such conditions [1]. Therefore, sodium stearate is a soap, not a synthetic detergent.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > Activity 4.12 > p. 76
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > CH COOH CH CH OH CH C C CH CH H O 3 3 2 3 2 3 2 Acid O (E - + - - - - - + thanoic acid) (Ethanol) (Ester) O > p. 73