Atoms, molecules, and ions in the gaseous state are characterized by a few physical properties. For example, all gaseous substances have high compressibility and are considered to be highly compressible. Another characteristic property of gaseous substances is that they exert pressure (on the walls of their container) of equal magnitude in all directions. Therefore, the pressure exerted by a gas on the walls of its container can be thought of as uniform in all directions.
The density of a gaseous substance is always much lower than that of its corresponding solid or liquid form. Gases do not have any definite shape or volume. Instead, they occupy the entire volume and shape of their container. Finally, no mechanical aid must be provided for the mixing of two different gaseous substances. They mix in an even and complete fashion in every proportion.