What differentiates one amino acid from the other?
a) amino group
b) r group
c) peptide group
d) carbonyl group

B) R group

Explanation: An aminoacid is composed by an amino group, an acid or carbonyl group and a side chain or R group, all bonded to a central carbon atom. Aminoacids are different between them for the R group and can be classified as: 1) Non-polar Neutral if the side chain is uncharged and non-polar (aliphatic or  cyclic). 2) Polar Neutral if the side chain contains amida, sulfur or hydroxyl groups. 3) Basic if the side chain contains other amino groups. 4) Acid if the side chain contains other carboxyl groups.

if you listed your answers right then i believe your answer is b.