Question

Why does the temperative of a substance remains constant during its mealting point or boiling point

Answer 1

beacause the heat supplied is used to break the bonds and kinetic energy is also imparted to next phase

Answer 2

For a long time scientists knew about the invariance of temperature during phase changes, but this phenomenon cannot be explained in terms of the usually observable variables, that is, the macroscopic or thermodynamic variables. To understand the WHY we need to look at the phase change from a microscopic point of view, in other words, we need to explain the observed behavior in terms of the motion of the atoms and molecules that form the substance.