Elemental Composition in Polymers

Steps:

• Identify key atoms in each polymer's repeating unit based on chemical structure.
• Nylon: polyamide with -CONH- linkage, includes C, H, O, N.
• Proteins: polypeptides from amino acids with -NH- and -CO- groups, include C, H, O, N, S.
• Terylene: polyester from ethylene glycol and terephthalic acid, includes C, H, O only.
• Clingfilm: typically PVC from vinyl chloride, includes C, H, Cl only.

Why B is correct:

• Proteins consist of amino acids featuring amine (-NH2) groups with nitrogen and carboxyl (-COOH) groups with oxygen, per their biochemical definition.

Why the others are wrong:

• A: Nylon's amide bonds (-CONH-) include both oxygen and nitrogen atoms.
• C: Terylene (PET) is a polyester with ester linkages (-COO-), containing only carbon, hydrogen, and oxygen.
• D: Clingfilm (PVC) has the formula -(CH2-CHCl)-, with carbon, hydrogen, and chlorine but no oxygen.

Final answer: B