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.
The number of known monosaccharides that exist in nature are
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 20
Glucose, fructose, ribose and galactose are common natural monosaccharides.
Monosaccharides are classified in two ways:
By functional group: an aldose contains an aldehyde group (glucose, ribose); a ketose contains a ketone group (fructose).
By number of carbon atoms: triose (3), tetrose (4), pentose (5), hexose (6), heptose (7).
The two are combined in the name: glucose is an aldohexose, fructose a ketohexose and ribose an aldopentose.
So the number of known monosaccharides that occur in nature is 20.
NCERT (2026-27 edition):
Monosaccharides
