Answer:
A gas expands spontaneously to fill its container.
Step-by-step explanation:
A gas would always expand spontaneously in any container to fill it up. Gas moves unaided to assume the volume of the space they are put into. Gas molecules are more random and posses more kinetic energy to drive their movements from one place to another. Gases would not require any energy input to make them move.
The volume of a container would then be the same as the volume of the gas that occupies it. Also, when pressure is applied to a gas, the volume reduces considerably according to "Boyle's law".
A homogeneous mixture would have their constituents existing in just one phase. Regardless of any chemical properties of gases, they form homogeneous mixtures.