Which of the following is NOT a monomer?

a. a glucose molecule

b. an amino acid

c. a protein

d. a nucleotide

C. A protein is not a monomer, it is a polymer consisting of repeating and similar sub units of monomers called amino acids.

A monomer is the basic unit of a polymer that when repeated, forms a complex unit now with different properties. Example is the polysaccharide with a monomer of a monosaccaride such as glucose. Protein is not a monomer since it can be divided still into smaller units called amino acids.