Question

Why does the temperature of substance remsin constant during the melting and boiling point?​

Answer 1

Because at that temperature the amount of extra heat which is being supplied to the substance is used in Breaking the intermolecular forces so the temperature remains constant and the until the state of matter changes the heat is used to break intermolecular forces and hence after the breaking of intermolecular forces temperature rises again.

Answer 2

substance make use of latent heat of fusion to overcome force of attraction between particle of solid to change into liquid during melting and latent heat of vaporization to overcome force of attraction between particle of liquid to change into vapour duirng boiling