Read the passage carefully and answer the questions:
Optically active polyhydroxy aldehydes or ketones or molecules which provide such units on hydrolysis are called carbohydrates. They can be broadly classified as monosaccharides, disaccharides and polysaccharides depending on their behavior towards hydrolysis. They are also classified as reducing or non reducing sugars. Another class of biomolecules is proteins which are polymers of twenty different amino acids linked by peptide bonds. Amino acids can be classified as acidic, basic or neutral depending on the relative number of amino and carboxyl groups in their molecule. The essential amino acids cannot be synthesized by our body and hence must be provided through diet. Nucleic acids are the polymers of nucleotides which in turn consist of a base, pentose sugar and phosphate. There are two types of nucleic acids namely, DNA and RNA which differ in the composition of sugar and a base.
Which of the following is non-reducing sugar?
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 — A non-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 | – |