The particles have the least energy in the solid state of matter. In solids, the particles are tightly packed together and can only vibrate about fixed positions, which means they have the least kinetic energy compared to liquids and gases. In contrast, particles in liquids have more kinetic energy as they can move past each other, while particles in gases have the most kinetic energy as they move freely and rapidly. Thus, solids have particles with the least energy among the three common states of matter: solid, liquid, and gas.