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 chain in an aminoacid is least polar? 
Select and explain. 
A. Methyl, B. Carboxyl, C. Amino, D. Phosphate
A: Methyl
Answer: A: Methyl 
Explanation: Methyl side chain is the least polar side chain associated with the nonpolar aminoacid alanine. Polarity of amino acid refers to the ability of the side chain of amino acid to interact with water at biologic pH. Alanine is the least hydrophobic non polar aminoacid due to the methyl side chain. Ref: Principles of Biochemistry and Biophysics By B.S. Chauhan, Pages 149-155