Step-by-step explanation:
When the water freezes, the variable which changes is the temperature because as we reduce the temperature, the particles will come closer to each other and the average kinetic energy of the particles of water decreases. Hence, the water freezes below 0°C.
In the case of melting, the temperature is increased which means that the particles move away from each other and the average kinetic energy of the particles of water at this temperature increases. Hence, the water melts above 100°C.