Question

why does a solid change into liquid on heating?

Answer 1

due to heating the temperature increases and when the temperature reaches the melting point, the element starts converting from solid state to liquid state

Answer 2

when a solid is heated they get heat energy and the particle starts vibrating ..

at a certain temperature particle start vibrating so much that their structure breakdowns and then the solid is converted into liquid form this is known as melting..

when a thing is solid the particles are tightly packed but when we heat it the particle starts vibrating and they expand this causes change from solid to liquid

hope it helps..