When a solid melts reversibly

When a solid melts there is

When a solid melts there is

When a solid melts, there is/are:

When a solid melts, there is:

When a solid melts, its temperature remains constant. Explain.

When a solid melts or a liquir boils, the temperature does not increase even when head is supplied .Where does not the energy go ?

When a solid melts or a liquir bolls, the temperature does not increase even when head is supplied .Where does not the energy go ?