Glucose on reaction with bromine water forms gluconic acid which confirms the presence of:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → -CHO group
Bromine water is a mild oxidising agent: it oxidises an aldehyde group to a carboxylic acid group but does not attack a ketone or the –OH groups. Glucose is oxidised by it to the six-carbon acid gluconic acid without loss of carbon:
\( \ce{HOCH2(CHOH)4CHO} \) + [O] (\( \ce{Br2} \) water) → \( \ce{HOCH2(CHOH)4COOH} \) (gluconic acid)
So the carbonyl group of glucose is present as an aldehydic (–CHO) group.
Why the other options are incorrect
Option (1) -COOH group — Incorrect. Glucose has no –COOH group; the –COOH of gluconic acid is produced by the oxidation.
Option (3) Five -OH groups — Incorrect. These are shown by acetylation: glucose with acetic anhydride gives a pentaacetate.
Option (4) Ketonic group — Incorrect. A ketone is not oxidised by mild bromine water, so this reaction rules a keto group out.
NCERT (2026-27 edition):
Structure of Glucose – …
