Question

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

Answer 1

Hello buddy.

This is all due to latent heat. The heat energy supplied is used up in changing the state of matter  and also this heat is used for breaking of several bonds or attractive forces.

Hope it helps you buddy
^_^

Answer 2

During the change of state, the particles of substance take some time to get energy to change hia state..
When it get that energy on that time the temp. remains constant...