Question

For any substance, why does the temperature remain constant during the change of state.

Answer 1

When something changes phase it takes or releases energy to break the intermolecular interactions. The heat is utilized in overcoming the particle-particle attraction forces and hence the temperature remains practically constant. Hope this helps

Answer 2

For any substance , the temperature remains constant during the change of state as the heat supplied to the body is used up in the proccess of breaking up of the inter and intramolecular bonds between the molecules and hence is used up as latent heat , causing no change in temperature.