The statement given in the question is TRUE; the side chain of an amino acid differentiates one amino acid from another.
Amino acids are the building blocks of proteins. Amino acids are nitrogenous compound, each one is made up of an acidic carboxylic group and a basic amino group. Each of the amino acids have unique side chains, that are quite different from those of other amino acids, this unique side chain is called R group. These side chains differentiate one amino acid from another one. Examples of R chains include: hydrogen, methyl group, etc. Each R group has different properties and functions.