Which characteristic is true for solids?

Solids are unique in their ability to maintain both shape and volume due to the close arrangement of their particles. In a solid, molecules are tightly packed together in a fixed structure, which allows them to vibrate in place but not move freely. This rigidity results in a definite shape that does not change unless a force is applied to break the bonds holding the structure together.

Additionally, solids have a definite volume because the particles are closely packed, preventing them from expanding to fill a container the way gases do.

In contrast, gases can diffuse quickly and easily due to their spread-out particles and high kinetic energy. Compressibility is a characteristic more associated with gases than with solids, as solids do not significantly change their volume under pressure. The mention of existence in gaseous form refers to a different state of matter and is not applicable to solids. Thus, the defining characteristic of solids being able to maintain both shape and volume stands out as the correct choice.