Identify amino acids containing non-polar, aliphatic R groups.
Phenylalanine, tyrosine, and tryptophan
Glycine, alanine, leucine
Histidine, arginine, Lysine
Serine, Cysteine, Threonine
The structures of Glycine, Alanine and Leucine are given below:
Glycine: HN+ _ CH 2 _ COO-
Alanine: H3N+ _ CH(CH3) _ COO-
Leucine: : H3N+ _ CH(C4H9) _ COO-
Hence, the correct answer is option 2.