solid's molecules have very high attraction forces, so the particles stay together and vibrate rather than any strong motion. Liquids have pretty strong attraction forces, but because they are weaker than solids, particles can move more freely, so they can slide against each other rather than vibrate. Gases have the least strong attraction forces compared to the two, so they can move everywhere, and as you know, gas is not constricted and it is everywhere, so gas is the answer.