Final answer:
Ionic compounds are most soluble in water due to their charged nature, which allows them to interact strongly with the polar water molecules. Polar molecules with hydrogen bonds can also dissolve well in water due to their ability to form hydrogen bonds. Nonpolar substances, on the other hand, generally do not dissolve in water.
Step-by-step explanation:
Among the substances listed, ionic compounds should be most soluble in water. This is because water is a polar solvent, which means that it has regions of positive and negative electrical charge. Ionic compounds are made up of positively charged ions (cations) and negatively charged ions (anions), which are attracted to the oppositely charged ends of water molecules, leading to dissolution.
Substances like polar molecules with hydrogen bonding also have good solubility in water, as they can form hydrogen bonds with the water molecules. However, nonpolar molecules, whether they have large molecular weights or not, typically do not dissolve well in water because they lack the charge properties needed to interact with the polar water molecules. These nonpolar molecules are described as hydrophobic, or 'water-fearing'.
In summary, water's ability to dissolve substances largely depends on the intermolecular interactions between the water molecules and the substance in question, abiding by the general rule that 'like dissolves like'. Therefore, the most soluble substances in water are those that are hydrophilic and can partake in similar intermolecular forces that the water itself experiences.