Glucose gets oxidized to gluconic acid on reaction with bromine water. This indicates the presence of:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Aldehyde group
Bromine water is a mild oxidising agent. It oxidises an aldehyde group (–CHO) to a carboxylic acid group (–COOH) without breaking the carbon chain, but it does not oxidise a ketone group. Glucose gives gluconic acid, a six-carbon acid:
\( \ce{CHO-(CHOH)4-CH2OH} \xrightarrow{\ce{Br2}\text{ water}} \ce{COOH-(CHOH)4-CH2OH} \)
Why the other options are incorrect
Option (2) Ketone group — Incorrect. A ketone group is not oxidised by bromine water, so a ketose such as fructose does not react with it.
Option (3) Carboxylic acid — Incorrect. Glucose has no –COOH group; the –COOH of gluconic acid is formed in the reaction.
Option (4) Anhydride group — Incorrect. Glucose has no anhydride group; its functional groups are one –CHO and five –OH groups.
NCERT (2026-27 edition):
Structure of Glucose – “… 4. Glucose gets oxidised to six carbon carboxylic acid (gluconic acid) on reaction with a mild oxidising agent like bromine water. This indicates that the carbonyl group is present as an aldehydic group.”