What characteristic of air allows it to be compressed?

Air can be compressed due to its nature as a mixture of gases, primarily nitrogen and oxygen, among others. Gases are characterized by having a lot of space between the molecules, which allows them to be pushed closer together when pressure is applied. When you apply pressure to a gas, the molecules can occupy a smaller volume, thus allowing for compression.

In contrast, liquids and solids have particles that are much more closely packed together, making them incompressible under normal conditions. A liquid, while it has some ability to compress slightly under extreme pressure, does not have the same characteristics as a gas when it comes to compressibility. Similarly, solids maintain their shape and volume, which prevents them from being compressed significantly. Compounds, on the other hand, refer to substances made of two or more elements chemically bonded together, and this term does not specifically speak to the compressibility of a substance in a gaseous state like air.

Overall, the ability of air to be compressed is fundamentally linked to it being a mixture of gases, where the molecular structure allows for flexibility in space under pressure.