Glycosidic linkage is formed by:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Elimination of water molecule
In a disaccharide or polysaccharide the monosaccharide units are joined through an oxygen atom: the –OH of the anomeric carbon of one unit and an –OH of the other unit combine and a molecule of water is lost. This oxide link is the glycosidic linkage, a condensation reaction.
\( \ce{C6H12O6 + C6H12O6 -> C12H22O11 + H2O} \)
For example, sucrose has a glycosidic linkage between C1 of α-D-glucose and C2 of β-D-fructose.
Why the other options are incorrect
Option (2) Addition of water molecule — Incorrect. Adding water is hydrolysis, which breaks the glycosidic linkage (sucrose → glucose + fructose); it does not form it.
Option (3) Elimination of ammonia molecule — Incorrect. Carbohydrates contain no nitrogen, so no \( \ce{NH3} \) can be lost; even the peptide bond of proteins forms by loss of water, not ammonia.
Option (4) Addition of ammonia molecule — Incorrect. Addition of \( \ce{NH3} \) would bring nitrogen into the molecule; the glycosidic link is an oxygen bridge.
NCERT (2026-27 edition):
Disaccharides
