The liquid with the lowest density will float on top of any liquid with a higher density. This is because density is a measure of mass per unit volume.

Here's why:

* Density and Buoyancy: An object submerged in a fluid experiences an upward buoyant force equal to the weight of the fluid displaced.

* Lower Density, Less Weight: A liquid with lower density means it has less mass packed into the same volume. Therefore, it weighs less than an equal volume of the denser liquid.

* Floating: When a less dense liquid is placed on top of a denser liquid, it displaces a volume of the denser liquid equal to its own volume. However, since it weighs less, the buoyant force acting on it is greater than its weight, causing it to rise and float on the surface.

Example: Oil (less dense) floats on water (more dense).