Which of the following is not a disaccharide ?

The correct answer is Option (1) → Cellulose

A disaccharide gives two monosaccharide units on hydrolysis; a polysaccharide gives a large number of them. All three common disaccharides have the formula \( \ce{C12H22O11} \) and are hydrolysed as:

    \( \displaystyle \ce{C12H22O11 + H2O} \xrightarrow{\ce{H+}} \ce{C6H12O6 + C6H12O6} \)

Cellulose is a long chain of thousands of β-D-glucose units joined by C1–C4 glycosidic links, \( \ce{(C6H10O5)_n} \). It is a polysaccharide, the main structural material of plant cell walls, so it is not a disaccharide:

    \( \displaystyle \ce{(C6H10O5)_n + nH2O} \xrightarrow{\ce{H+}} \ce{nC6H12O6} \)

• Option (1) Cellulose — Not a disaccharide. It is a polysaccharide of thousands of β-D-glucose units.

• Option (2) Lactose — A disaccharide. Lactose, the sugar of milk, is made of β-D-galactose and β-D-glucose.

• Option (3) Maltose — A disaccharide. Maltose is made of two α-D-glucose units joined C1–C4.

• Option (4) Sucrose — A disaccharide. Sucrose is made of α-D-glucose and β-D-fructose.

NCERT (2026-27 edition):
Classification of Carbohydrates – “… (ii) Oligosaccharides: Carbohydrates that yield two to ten monosaccharide units, on hydrolysis, are called oligosaccharides. They are further classified as disaccharides, trisaccharides, tetrasaccharides, etc., depending upon the number of monosaccharides, they provide on hydrolysis. Amongst these the most common are disaccharides.
(iii) Polysaccharides: Carbohydrates which yield a large number of monosaccharide units on hydrolysis are called polysaccharides. Some common examples are starch, cellulose, glycogen, gums, etc.”

Note: The same/similar question has been asked in different years by NTA as per the details given below: