Here's why:
* Solids have a fixed shape: The particles in a solid are tightly packed together in a regular arrangement. This arrangement gives the solid a definite shape that doesn't change easily.
* Solids have a fixed volume: The particles in a solid are close together, and they vibrate in place but don't move freely. This fixed arrangement means that the volume of the solid remains constant.
Let me know if you have any more questions about states of matter!
