Amino acid in Zwitter ionic form shows

The correct answer is Option (3) → Amphoteric behaviour

An amino acid has both an acidic carboxyl group and a basic amino group. In aqueous solution the carboxyl group loses a proton and the amino group accepts a proton, giving a dipolar ion called the zwitter ion:

    \( \ce{H2N-CH(R)-COOH} \) ⇌ \( \ce{H3N^{+}-CH(R)-COO^{-}} \)

The –\( \ce{COO^{-}} \) end can take up a proton from an acid and the –\( \ce{NH3^{+}} \) end can give a proton to a base. Reacting with both acids and bases is amphoteric behaviour.

Why the other options are incorrect

• Option (1) Acid behaviour — Incorrect. The zwitter ion can act as an acid (through –\( \ce{NH3^{+}} \)), but it also acts as a base, so “acid” alone is incomplete.

• Option (2) Basic behaviour — Incorrect. The zwitter ion can act as a base (through –\( \ce{COO^{-}} \)), but it also acts as an acid, so “basic” alone is incomplete.

• Option (4) Neutral behaviour — Incorrect. The zwitter ion carries no net charge, but it is not chemically inert; it reacts with both acids and bases.

NCERT (2026-27 edition):
Classification of Amino Acids – “… Amino acids are usually colourless, crystalline solids. These are water-soluble, high melting solids and behave like salts rather than simple amines or carboxylic acids. This behaviour is due to the presence of both acidic (carboxyl group) and basic (amino group) groups in the same molecule. In aqueous solution, the carboxyl group can lose a proton and amino group can accept a proton, giving rise to a dipolar ion known as zwitter ion. This is neutral but contains both positive and negative charges.

In zwitter ionic form, amino acids show amphoteric behaviour as they react both with acids and bases.”