Final answer:
Gases are highly compressible due to the continuous motion of molecules and the large amount of empty space between them. When pressure is applied, gas molecules can be forced closer together, resulting in a smaller volume.
Step-by-step explanation:
Gases are highly compressible because they are composed of molecules that are in continuous motion and are highly separated, allowing for the gas to be easily compressed.
The large amount of empty space between gas molecules allows for gases to be compressed when pressure is applied. For example, when a gas-filled container is squeezed, the gas molecules are forced closer together, resulting in a smaller volume.