Which of the followings is NOT a monosaccharide?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Sucrose
Carbohydrates are classified by their behaviour on hydrolysis. A monosaccharide cannot be hydrolysed into a simpler polyhydroxy aldehyde or ketone. An oligosaccharide gives two to ten monosaccharide units (a disaccharide gives two), and a polysaccharide gives a large number of them.
Sucrose is a disaccharide: on hydrolysis with dilute acid or the enzyme invertase it gives one molecule each of glucose and fructose:
\( \displaystyle \ce{C12H22O11}\,(\text{sucrose}) + \ce{H2O} \xrightarrow{\ce{H+}} \ce{C6H12O6}\,(\text{glucose}) + \ce{C6H12O6}\,(\text{fructose}) \)
Option (1) Glucose — A monosaccharide. Glucose, \( \ce{C6H12O6} \), is an aldohexose and cannot be hydrolysed further.
Option (2) Fructose — A monosaccharide. Fructose, \( \ce{C6H12O6} \), is a ketohexose, also a single sugar unit.
Option (3) Ribose — A monosaccharide. Ribose, \( \ce{C5H10O5} \), is an aldopentose, the sugar of RNA.
Option (4) Sucrose — Not a monosaccharide. It is a disaccharide; hydrolysis splits it into glucose and fructose.
NCERT (2026-27 edition):
Monosaccharides
