Final answer:
Lipids, such as oil, do not mix with water because they are hydrophobic, nonpolar molecules.
Step-by-step explanation:
Lipids, such as oil, do not readily mix with water due to their hydrophobic nature. Lipids are nonpolar molecules, which means they do not have a charge and do not readily interact with water molecules that are polar. Water is a polar molecule, meaning it has a positive and negative end, which allows it to form hydrogen bonds with other polar molecules but not with nonpolar molecules.