Salad oil is a nonpolar molecule, while water is a polar molecule. Nonpolar molecules are molecules that do not have a net electrical charge, while polar molecules are molecules that have a net electrical charge. The difference in polarity between salad oil and water causes them to be immiscible, meaning that they do not dissolve in each other.

When salad oil and water are mixed, the oil droplets will form a separate layer on top of the water. This is because the oil droplets are less dense than water, so they will float to the surface. The oil droplets will also be surrounded by a layer of water molecules, which will help to keep them from mixing with the water.

The addition of an emulsifier can help to dissolve salad oil in water. An emulsifier is a molecule that has both a polar and a nonpolar end. The polar end of the emulsifier will dissolve in water, while the nonpolar end will dissolve in salad oil. This will help to break up the oil droplets and allow them to mix with the water.

Some common emulsifiers include soap, detergent, and egg yolks. These emulsifiers can be used to make salad dressings, mayonnaise, and other sauces.