Question

why does the temperature remain constant during change of physical state of matter?​

Answer 1

Since the heat is used to overcome the force of attraction, the temperature of the substance does not change. The heat energy absorbed in this case is called as the latent heat. The temperature of the substance remains equal to the latent heat provided to or released by it. That's why for any substance, the temperature remain constant during the change of state.

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Answer 2

When a solid melts to form liquid the temperature remains constant because change in state takes place and the latent heat is used up in overcoming the forces of attraction between the particles of solid.