water molecules separate positive and negative ions from one another by forming

covalent bonds,

ionic bonds

valence shells

hydration shells

It forms a solution. Since solution isn't one of the answers, hydratin shells is the next best answer. OR, you can think about it this way.
Covalent bonds, ionic bonds, and valence shells don't have anything to do with dissolving a solute in a solvent such as water. So hydration shells is the only answer left.

Actually, the correct answer is "ionic bonds". When a substance dissolves in water, the water molecules surround the individual ions of the solute, effectively separating them from each other. This process is known as hydration or solvation. The water molecules form temporary electrostatic attractions with the positive and negative ions, which helps to keep the ions dispersed in the solution. This is why water is often referred to as a universal solvent, as it can dissolve a wide range of substances by breaking their ionic bonds and surrounding the resulting ions with hydration shells.