Consider the following statements about some α-amino acids.
(A) Lysine, whose side chain is H2N–(CH2)4–, is a basic amino acid.
(B) Aspartic acid, whose side chain is HOOC–CH2–, is a neutral amino acid.
(C) Alanine, whose side chain is –CH3, is a neutral amino acid.
(D) Arginine is an amino acid that must be obtained through diet.
Which of the statements given above are correct? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A), (C) and (D) only
Every α-amino acid has one –NH2 and one –COOH group on the α-carbon; the side chain decides whether there are extra ones. Equal numbers of amino and carboxyl groups make an amino acid neutral, more amino groups make it basic, and more carboxyl groups make it acidic.
(A) Lysine, whose side chain is H2N–(CH2)4–, is a basic amino acid. — True. The side chain adds a second –NH2 group: two amino groups, one carboxyl group.
(B) Aspartic acid, whose side chain is HOOC–CH2–, is a neutral amino acid. — False. The side chain adds a second –COOH group: one amino group, two carboxyl groups, so aspartic acid is acidic.
(C) Alanine, whose side chain is –CH3, is a neutral amino acid. — True. The methyl group adds neither group: one amino group, one carboxyl group.
(D) Arginine is an amino acid that must be obtained through diet. — True. Arginine is marked with an asterisk in the table of natural amino acids; it is an essential amino acid, which the body cannot synthesise.
NCERT (2026-27 edition):
10.2.2 Classification of Amino Acids – “Amino acids are classified as acidic, basic or neutral depending upon the relative number of amino and carboxyl groups in their molecule. Equal number of amino and carboxyl groups makes it neutral; more number of amino than carboxyl groups makes it basic and more carboxyl groups as compared to amino groups makes it acidic. … On the other hand, those which cannot be synthesised in the body and must be obtained through diet, are known as essential amino acids (marked with asterisk in Table 10.2).”
Table 10.2: Natural Amino Acids