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

Question

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.