The structure of the gluconic acid obtained from oxidation of glucose…

The correct answer is Option (1) → COOH–(CHOH)₄–CH₂OH

Glucose is an aldohexose: an open chain of six carbon atoms with an aldehyde group at C-1, four secondary alcohol groups (CHOH) and a primary alcohol group (\( \ce{CH2OH} \)) at C-6. A mild oxidising agent such as bromine water oxidises only the aldehyde group to a carboxyl group and leaves the alcohol groups untouched. The product, with all six carbons, is gluconic acid:

So gluconic acid is COOH–(CHOH)₄–CH₂OH.

Why the other options are incorrect

• Option (2) COOH–(CHOH)₄–CH₂COOH — Incorrect. This has seven carbon atoms; oxidation cannot add a carbon to the six-carbon chain of glucose.

• Option (3) CHO–(CHOH)₄–COOH — Incorrect. Here the aldehyde group is kept and the primary alcohol is oxidised (glucuronic acid). Bromine water attacks the aldehyde group first, so this is not its product.

• Option (4) COOH–(CHOH)₄–COOH — Incorrect. This is saccharic acid, formed when a strong oxidising agent, nitric acid, oxidises both ends: \( \ce{OHC-(CHOH)4-CH2OH} \xrightarrow{\ce{HNO3}} \ce{HOOC-(CHOH)4-COOH} \).

NCERT (2026-27 edition):
Glucose – …