An aqueous solution of glucose behaves as an aldehyde because

Because It's cyclic hemiacetal and the predominant form is in equilibrium with the free aldehyde form. as glucose has an aldehyde group and five hydroxyl group and can form an intramolecular cyclic hemiacetal. In aqueous solution, glucose exists in open and closed forms.when the process of converting the close form to open form and them back to the close form the rotate of the c1 and c 2 happened, that rotation produces the two anomers α & β. So the equilibrium of α & β in solution is a resulting of this mutarotation. In glucose, the anomer β is more predominate than α anomer.

Ur e n d is not real

Ithink is d. physical property