Nylon 2-nylon 6 has a repeat unit $- [NH - CH X_{2} - CO - NH - (CH X_{2}) X_{5} - CO] X^{-}$ of molar mass 170 g/mol and contains two amide bonds per repeat unit. The mass of water needed to hydrolyse every amide bond in $85.0 g$ of the polymer (end groups neglected; H2O = 18) is

Answer: B

85.0 g / 170 = 0.500 mol of repeat units, each with 2 amide bonds, so 1.00 mol of bonds needs 1.00 mol of water = 18.0 g.