Answer:
You can create a sketch about two fluids inside a glass. You will put oil and water inside, there you will observe how both fluid don't mix each other, even is you mix them with a tool, you won't be able to do it. The oil always is gonna be separate it from the water.
In thar sketch, you will label the oils as less dense, and the water as more dense, because oil density is 920 kilograms per cubic meters, and water is 1000 kilograms per cubic meters. That's the reason why the oil is gonna be on the surface, above the water. According to physics, the less dense fluid always floats over the more dense fluid.