O-linked D-mannose can form a glycosidic bond with any sugar that has a free anomeric carbon. Therefore it could theoretically form a glycosidic bond with all of the following sugars EXCEPT:A.galactose.B.ribose.C.lactose.D.sucrose.

The answer is D. Sucrose.

Here's why:

A glycosidic bond is a type of covalent bond that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate.

For a glycosidic bond to form, at least one of the sugars needs to have a free anomeric carbon. An anomeric carbon is a carbon in a sugar molecule that can take on different configurations (alpha or beta).

A. Galactose and B. Ribose both have free anomeric carbons, so they could theoretically form a glycosidic bond with O-linked D-mannose.

C. Lactose is a disaccharide composed of galactose and glucose, both of which have free anomeric carbons, so it could also theoretically form a glycosidic bond with O-linked D-mannose.

D. Sucrose, however, is a disaccharide composed of glucose and fructose. In sucrose, the anomeric carbons of both the glucose and fructose units are involved in the glycosidic bond, meaning they are not free to form additional bonds. Therefore, sucrose could not form a glycosidic bond with O-linked D-mannose.