Comprehension:
Biomolecules
Sugars are the carbohydrates which are sweet in nature and one such example is sucrose. Carbohydrates are classified based on their behavior towards hydrolysis. Carbohydrates can also be classified as reducing or non-reducing sugars based on their behavior towards Fehling's reagent and Tollens' reagent. Monosaccharides can also be classified based on the number of carbon atoms as well as the functional group present in the structure. The two monosaccharides are joined through a special linkage. Carbohydrates are optically active compounds which contain polyhydroxy aldehyde groups or ketones or the compounds which produce such units on hydrolysis.
Among the following carbohydrates, the non-reducing sugar is
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Sucrose
A reducing sugar reduces Fehling’s solution and Tollens’ reagent. It can do so only if it has a free aldehyde or ketone group (a free hemiacetal carbon that can open to the carbonyl form). All monosaccharides are reducing sugars. A disaccharide is reducing only if one of its units still has this group free after the glycosidic linkage is formed.
Option (1) Maltose — A reducing sugar. The C1 of its second glucose unit is free.
Option (2) Glucose — A reducing sugar. A monosaccharide with a free aldehyde group.
Option (3) Sucrose — Not a reducing sugar. C1 of α-D-glucose is joined to C2 of β-D-fructose, so both reducing groups are used in the linkage. On hydrolysis it gives the two reducing monosaccharides: \( \ce{C12H22O11 + H2O -> C6H12O6 + C6H12O6} \) (D-(+)-glucose and D-(−)-fructose).
Option (4) Fructose — A reducing sugar. A monosaccharide with a free ketone group.
NCERT (2026-27 edition):
Disaccharides – …
Note: The same/similar question has been asked in different years by NTA as per the details given below:
| 2026 | 2025 | 2024 | 2023 | 2022 |
|---|---|---|---|---|
| 30-05 S2 26-05 S2 24-05 S2 | 28-05 S2 21-05 S1 | – | 01-06 S3 | – |