Final answer:
Glucose, galactose, and fructose are hexoses, with glucose and galactose forming six-membered rings and fructose forming a five-membered ring. They are all monosaccharides, while maltose is a disaccharide comprising two glucose units.
Step-by-step explanation:
The ring-shaped (hexagonal and pentagonal) simple sugars (monosaccharides) you've mentioned are all hexoses, which have six carbon atoms. Glucose and galactose are aldoses with six-membered rings. Although fructose is also a hexose, it forms a five-membered ring and is a ketose. Maltose is not a monosaccharide, but a disaccharide, composed of two glucose units.
In aqueous solution, these monosaccharides are predominantly found in their cyclic forms. Glucose can exist in two different ring forms, known as alpha (α) or beta (β), depending on the position of the hydroxyl (OH) group around the anomeric carbon (carbon 1). Fructose, though a hexose, forms a five-membered ring, differing from glucose and galactose's six-membered structure.