Compressibility refers to the ability of a substance to decrease in volume under pressure.

Gases have very weak intermolecular forces, meaning the molecules are widely spaced and can move freely. When pressure is applied, the molecules are forced closer together, resulting in a decrease in volume.

Liquids are much less compressible than gases. While they can be compressed slightly, the molecules are much closer together, and the intermolecular forces are stronger.

Solids are generally considered incompressible. Their molecules are tightly packed, and the intermolecular forces are very strong, making it difficult to compress them significantly.

Therefore, gases are the most compressible state of matter.