Question

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

Answer 1

yes for any substance temperature remains constant during the state change as all the energy is being used to change the state by breaking the previous bonds

Answer 2

for any substance the temperature as the heat(energy)
provided after reaching the boiling point helps in changing the state of matter and is called the latent heat of fusion(from solid to liquid )
and latent heat of vaporisation (from liquid to gases...