Question

Why does the temp of substance remains constant during its melting point and boiling point

Answer 1

Changing liquid to gas. When a liquid—such as water—is heated at a constantpressure, some of its molecules get enough KE to escape the liquid. ... Thus, moreheat energy is needed to cause other molecules to escape. This keeps the liquid at atemperature slightly below that of the boiling point

Answer 2

hey friend,
this happens because the latent heat used in this process is disolved.