An aqueous solution of a carbohydrate gives a dark blue colour with iodine solution. The carbohydrate is:

Step-by-step solution

Starch consists of two components: amylose and amylopectin. Amylose is a linear polymer of -D-glucose and forms a helical structure in water. When iodine solution is added, iodine molecules get trapped inside the helical structure of amylose, forming an intense dark blue coloured complex. Other carbohydrates like glucose, fructose, and sucrose do not have this helical structure and therefore do not give a blue colour with iodine solution. Answer: starch