Final answer:
Liquids fill from the bottom of a container because their molecules move but not enough to fill the entire container while gas fills the entire container because its molecules move freely in all directions.
Step-by-step explanation:
The reason why a liquid fills from the bottom of a container while a gas fills the entire container has to do with the behavior and properties of these matter states. Liquids and solids resist being compressed due to their molecules being close together.
A liquid stays at the bottom of a container because its molecules are free to move, but not enough to fill the entire container. When a liquid is poured into a container, it takes the shape of the container from the bottom up, holding itself together due to the mutual attraction between the molecules.
On the other hand, gases have molecules that are free to move in all directions, which allows them to expand and fill all the available space. When we put gas into a container, it expands to fill the entire volume of the container irrespective of its shape. This is due to the relatively weak forces of attraction between the gas molecules and high speed of molecules which help them to move in all directions.
Learn more about States of matter