The main factor that makes amino acids unique from one another is the R group. Each amino acid has a different R group, also known as a side chain, attached to the central carbon atom. The R group can vary in size, structure, and chemical properties, which contributes to the specific characteristics and functions of each amino acid. Additionally, amino acids all have the same basic structure, consisting of an amino group (-NH2), a carboxyl group (-COOH), and a hydrogen atom attached to a central carbon atom. However, it is the R group that differentiates one amino acid from another. So, the correct answer is: the R group.
