Glycosidic linkage is formed by:

Elimination of water molecule

Glycosidic linkage is formed by the elimination of a water molecule. So the answer is (1).

To form a glycosidic linkage, the hemiacetal or hemiketal group of one sugar molecule reacts with the hydroxyl group of another sugar molecule. This reaction is catalyzed by enzymes called glycosyltransferases. The reaction results in the formation of a new carbon-oxygen bond (the glycosidic linkage) and the release of a water molecule.

Here is an example of a glycosidic linkage formation reaction between two glucose molecules:

\(α-D-glucose + β-D-glucose → maltose + H_2O\)

In this reaction, the hemiacetal group of α-D-glucose reacts with the hydroxyl group of β-D-glucose to form a glycosidic linkage between carbon 1 of α-D-glucose and carbon 4 of β-D-glucose. A water molecule is released in the process.

Glycosidic linkages are very important in biochemistry. They are found in many different types of carbohydrates, including disaccharides, polysaccharides, and glycoproteins. Glycosidic linkages play a role in energy storage, cell-cell communication, and immunity.