this is because particles in solids are packed very closely together, thus , the particles collide with each other frequently and thus transfer of energy is faster. however, particles in liquid are closely packed but not as close as in solid so the particles do not collide as frequently. thus, transfer of energy slower than in solid. furthermore, the particles in gas are spaced far apart from each other, thus the particles don't collide with each other frequently, thus transfer of energy is very slow in gas.
