Elementary Idea of ??-amino Acids — Prelims Questions

Which of the following statements about alpha-amino acids is INCORRECT?

Which of the following amino acids has a nonpolar, aliphatic R-group?

At a pH significantly lower than its isoelectric point (pI), an amino acid will predominantly exist in which form?

Which of the following amino acids is considered essential for humans?

Which of the following amino acids contains a sulfur atom in its R-group?

Which of the following amino acids is an example of an acidic amino acid at physiological pH?