Which of the following statements about the polarity of the R groups in amino acids are correct?
I) All amino acids with hydroxyl (-OH) groups in their R groups are classified as polar.
II) Amino acids with aromatic rings in their R groups are always nonpolar.
III) Amino acids with charged R groups can be classified as either polar or nonpolar.
IV) Sulfur-containing R groups in amino acids are generally nonpolar.
V) Amino acids with carboxyl (-COOH) groups in their R groups are classified as nonpolar.

• A. I and IV
• B. I and II
• C. I, II, and IV
• D. I, III, and IV

Answer: (A)