Caprolactam is the monomeric unit of -
Nylon 6
The explanation for the correct option
Caprolactam is the monomericunit of Nylon-6.
(a) Nylon-6 is the repetitive unit of caprolactam
The explanation for the incorrect options
(b) Nylon-6,6 has two constituent units one is adipic acid and the second is hexane diamine.
(c) Nylon-2-nylon-6 has two constituent units one is glycine and another is aminocaproic acid.
Hence, option (A) is the correct answer.