Each liquid has a different density, meaning that although the volume is the same, the mass of each liquid is different. Density = Mass / Volume.
The higher the density, the more compact the substance is, e.g. Iron is more dense than water.
The glycerol is much denser than water, so the water floats above it.
Is the vegetable oil more or less dense than the water? Why do some objects sink and others float?
Weird Fact: The planet Saturn is less dense than water. A big enough ocean could make it float!
Solid water (ice) floats because it is less dense than water as a liquid. Very unusual for a chemical.