If you were asked to build a polymer that is two monomers long (ok, that wouldn’t really be a polymer, but let’s ignore that for the moment), and you could use two different types of monomers, "A" and "B", how many different polymers could you build?

A monomer is a small molecular mass molecule that is attached to other monomers, sometimes hundreds or thousands, by chemical bonds, usually covalent, forming macromolecules called polymers. Polymerization is the process of covalent bonding of the smallest monomers to the polymer. During polymerization, chemical groups are lost from the monomers so that they can bond. Examples are:

Amino acids are the monomers of proteins.
Nucleotides are the monomers of nucleic acids.
Monosaccharides are the monomers of polysaccharides.
Lipid monomers are the monomers of fatty acids

In this case, if we have the A and B monomers, the combinations can be A attached to A, A attached to B, B attached to B and B attached to A. This gives us a total of 4 different polymers.