A nylon 6 chain has a molar mass of $56500 g mo l^{- 1}$ (end groups ignored). The repeat unit is $- [NH (CH X_{2}) X_{5} CO] X^{-}$ (formula $C X_{6} H X_{11} NO$ ; C 12, H 1, N 14, O 16), formed by ring-opening polymerisation of caprolactam. The number of caprolactam molecules consumed per chain and the net number of $H X_{2} O$ molecules released per chain are

Answer: A

Repeat-unit mass

= 6 (12) + 11 + 14 + 16 = 113

, so

56500/113 = 500

repeat units. Caprolactam has the same formula

C X_{6} H X_{11} NO

as the repeat unit; ring opening is addition-like and releases no water. So 500 molecules are consumed and no water is released.