When two monomers are joined together to make a polymer, what other molecule is produced?

Water (H₂O) Molecule

Explanation:

This is why this process is usually called a dehydration/condensation process. The reason a water molecule is produced as a by-product is that one end of the one monomer involved in the bonding releases an - OH while the other monomer releases an - H before a bond joining the two monomers is formed. These two radicals combine to form a water molecule (OH⁻ + H⁺ → H₂0).