What is the definite shape and volume for solid, liquid, and gas?
The physical state for any substance is dependent upon the kinetic energy contained within the atoms and molecules that make it up.
Solids have the lowest amount of kinetic energy. The particles that make up a solid are packed close together and are rigid, so that they can only vibrate in place. Solids have a definite shape and a definite volume.
Liquids have more kinetic energy, so their particles are less rigid and can slide around one another, which allows liquids to flow. Liquids have no definite shape, so that they take the shape of their container, except for the surface, which is flat, but they do have a definite volume.
Gases have more kinetic energy than liquids, so their particles move very rapidly. Gases expand to fill their container, so they have no definite shape and no definite volume.