Let us analyze each statement:
Incorrect. Glucose is soluble in water due to the presence of multiple hydroxyl ($-$OH) groups, not because of the aldehyde functional group. The hydroxyl groups form hydrogen bonds with water, making glucose highly soluble.
Correct. In aqueous solution, glucose exists in equilibrium between its open-chain form and cyclic isomeric forms ($\alpha$- and $\beta$-D-glucose).
Correct. Glucose is classified as an aldohexose because it contains six carbon atoms (hexose) and an aldehyde group (aldo).
Correct. Glucose is one of the two monomeric units of sucrose, the other being fructose.
Final Answer: (1)