Which state of matter has the most energy?

The answer is very simply gas. Gas has the most energy because it has the most space between particles to be able to move around. When given the space to move about, particles will do so. Solids have the least amount of energy because the molecules are tightly packed leaving very little room to move.

The state of liquid is right between solids and gasses—liquids' particles have space to move but they don't move as quickly. Keep in mind that when you heat matter up, the molecules begin to move faster.

The gas state of matter has the most energy because of how freely the molecules move. Matter is a physical substance of which there are three, and they are solid, liquid, and gas. Solid matter is very compact with the particles very close together and not much movement; therefore, no action, no energy.

Liquid matter does have some movement but certainly not as free as gas so not as much energy and more mobility than solid so there is more energy there. Matter in a gaseous state has both variable volume and shape, adapting both to fit its container. Its particles are neither close together or fixed in place. Because the particles have room to move there is a lot of energy spent. Not only will gas conform to the shape of its container. It will also augment to fill the vessel.