Ionic substances are highly soluble in water. CuSO4 is an ionic salt composed of Cu2+ and SO42- ions. These ions are solvated in water hence the salt easily dissolves in the surrounding water molecules. this accounts for the fact that it is the most soluble of the five substances in water. 2-butanol contains the -OH group which interacts with water by hydrogen bonding. This accounts for the miscibility of alkanols with water in all proportions. however, this solubility in water decreases as the alky backbone increases. hence C4H9OH is less soluble in water that 2-butanol. Alkanes are usually not quite soluble in water but again solubility decreases with increase in the alky backbone hence propane is less soluble in water than ethane.
