Which state of matter is considered the least compressible?

The state of matter that is considered the least compressible is solid. Solids have a fixed volume and shape due to the closely packed arrangement of their particles, which are held together by strong intermolecular forces. This close packing means that there is very little space between the particles, making it extremely difficult to compress them further.

In contrast, gases can be significantly compressed because their particles are far apart and move freely; this allows them to fill the volume of their container. Liquids, while less compressible than gases, still have some degree of compressibility due to the ability of their particles to move slightly closer together under pressure, though they are more tightly packed than gases. Plasma, which consists of highly energized particles, behaves similarly to gases and is also compressible. Therefore, solids stand out as the least compressible state because their rigid structure resists any attempts to reduce their volume.