A+B → Nylon 6, 6 Predict A and B:

The correct answer is Option (4) → Hexamethylene diamine + adipic acid

Nylon 6,6 is a polyamide made by condensation polymerisation of hexamethylenediamine with adipic acid under high pressure and at high temperature. The two numbers show that each monomer has six carbon atoms:

    nH₂N(CH₂)₆NH₂ + nHOOC(CH₂)₄COOH → [–\( \ce{NH(CH2)6NH-CO(CH2)4CO} \)–]_n + 2nH₂O

Each –\( \ce{NH2} \) and –COOH pair joins by an amide (–CO–NH–) link and loses a water molecule.

Why the other options are incorrect

• Option (1) Ethylene glycol + adipic acid — Incorrect. A diol and a diacid join by ester links and give a polyester, not a nylon (polyamide).

• Option (2) Pentamethylene diamine + adipic acid — Incorrect. A five-carbon diamine would give a polyamide with 5 and 6 carbons in its units, not nylon 6,6.

• Option (3) Hexamethylene amine + tartaric acid — Incorrect. A mono-amine has only one –\( \ce{NH2} \) group and cannot build a chain; tartaric acid is not a monomer of nylon.

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):
Polyamides – “… (i) Nylon 6,6: It is prepared by the condensation polymerisation of hexamethylenediamine with adipic acid under high pressure and at high temperature.”