Final answer:
Ionic compounds have the highest molar solubility in pure water.
Step-by-step explanation:
In pure water, the compound with the highest molar solubility would be ionic compounds. Ionic compounds dissolve in polar solvents like water due to the attraction between the positive cation and the negative end of the water molecule, as well as the attraction between the negative anion and the positive end of the water molecule. Nonpolar substances and gases have low solubility in water, while insoluble salts do not dissolve in water at all.