During the phase change does the average kinetic energy of the molecules of the substance increase?
How does the (a) average kinetic energy (b) average potential energy of molecules of a substance change during its change in phase at a constant temperature, on heating ?
(a) What do you understand by the change of phase of a substance?
(b) Is there any change in temperature during the change of phase?
(c) Does the substance absorb or liberate any heat energy during the change of phase?