This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Which of the following side chains is least polar 
Select and explain. 
A. Methyl, B. Carboxyl, C. Amino, D. Phosphate
A: Methyl
Answer: A: Methyl 
Explanation: Side chain (R) of amino acid which have pure alkyl groups (e.g. methyl), or pure aromatic group, are nonpolar.
Side chain (R) of amino acid which have functional groups, such as hydroxyl, carboxyl, amino, amides and acids, imparts more polar characteristic to amino acid.