The carbohydrate that gives a dark blue color with iodine solution is starch. Starch is a complex carbohydrate that is made up of many glucose units linked together. When starch is dissolved in water, it forms an aqueous solution.

Iodine solution is commonly used as a chemical indicator to test for the presence of starch. It reacts with the starch molecules to form a deep blue or purple complex. This reaction is known as the iodine-starch complex.

The reaction between iodine solution and starch is based on the formation of a helical structure in starch molecules. Starch consists of two types of glucose polymers - amylose and amylopectin. Amylose is a linear chain of glucose units, while amylopectin is a branched chain. Both amylose and amylopectin can form helical structures.

When iodine molecules come into contact with the helical structure of starch, they become trapped within the helix. This results in the formation of the iodine-starch complex, which has a dark blue or purple color. The intensity of the color depends on the concentration of starch in the solution.

In contrast, other carbohydrates like sucrose, fructose, and glucose do not give a dark blue color with iodine solution. This is because they do not have the same helical structure as starch and do not form the iodine-starch complex. Sucrose is a disaccharide made up of glucose and fructose, while fructose and glucose are monosaccharides.

Therefore, when an aqueous solution of a carbohydrate gives a dark blue color with iodine solution, it can be concluded that the carbohydrate is starch. This property of starch to react with iodine solution and form a dark blue complex is widely used in various laboratory tests and experiments.