Read the passage carefully and answer the questions.
Biomolecules are the organic compounds present as an essential constituents of living organisms in different cells. The molecules are generally termed as macromolecules, which are carbohydrates, enzymes, nucleic acids, amino acids and proteins etc. Carbohydrates are classified as sugars and non-sugars include sucrose, glucose, fructose, starch and cellulose. Enzymes are coordinated with various chemical reactions in nucleic acid. Nucleic acids are found in living organisms made up of proteins and natural polymers. Two types that are generally found in biological systems are DNA and RNA nucleic acid. Amino acids are bifunctional groups of carboxyl and amino groups. Proteins are a class of biologically important compounds. They are crucial to virtually all processes in living systems. Some of them are hormones, which serve as chemical messengers that coordinate certain biochemical activities.
The zwitterionic form of amino acid is
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (B)
An amino acid has an acidic carboxyl group and a basic amino group in the same molecule. In water the carboxyl group loses a proton and the amino group accepts it, giving a dipolar ion called a zwitter ion:
\( \displaystyle \mathrm{H_2N{-}CH(R){-}COOH} \ce{<=>} \mathrm{{}^{+}H_3N{-}CH(R){-}COO^{-}} \)
Structure (B), \( \mathrm{{}^{+}H_3N{-}CH(R){-}COO^{-}} \), is this form.
Why the other options are incorrect
Option (1) (A) — Incorrect. Structure (A), \( \mathrm{H_2N{-}CH(R){-}COO^{-}} \), has only the negative carboxylate; it is the anion present in basic solution.
Option (3) (C) — Incorrect. Structure (C), \( \mathrm{{}^{+}H_3N{-}CH(R){-}COOH} \), has only the positive ammonium group; it is the cation present in acidic solution.
Option (4) (D) — Incorrect. Structure (D), \( \mathrm{H_2N{-}CH(R){-}COOH} \), carries no charge at all; it is the un-ionised form, which is not how amino acids exist in water or in the crystal.
Note: It seems that there is a mistake in the original NTA paper, which prints “Amino acids are bifunctional groups of carboxyl and amino groups” in the passage when it should read “Amino acids are bifunctional compounds containing carboxyl and amino groups”. It also prints “Nucleic acids are found in living organisms made up of proteins and natural polymers” when it should read “Nucleic acids are natural polymers of nucleotides found in living organisms”, and “Enzymes are coordinated with various chemical reactions in nucleic acid” when it should read “Enzymes catalyse the chemical reactions in living systems”.
NCERT (2026-27 edition):
Classification of Amino Acids – …
