Question

A liquid does not fill its container completely .why?

Answer 1

The atoms and molecules in gases are much more spread out then in solids or liquids. They vibrates and move freely at high speeds.A gas will fill any container but if the container is not sealed the gas will escape. Gas can be compressed much easily than a liquid or solid.
"Hope,I help you.

Answer 2

The filling process of any type of container is heavily dependent on the physical properties of the substance which we are using for the filling process.

Similarly when we try to fill a container with any liquid substance, the container doesn't fill completely because the molecular gaps of the liquid substances are very large.

That's why the liquids are unable to occupy the total space of a container.