Why does a solid change to liquid when heat is added

It is due to the change in the position of the molecules of the solid substance.

Explanation:

All solid substances contains molecules that are tightly packed together. When heat is applied to this solid substances, the molecules of the substance tends to vibrate away from their mean fixed position as such causes a change in the state of the solid matter into a liquid. The process by which a solid changes to liquid is known as Melting or Fusion

b.transmitters send radio waves, and receivers capture radio waves.

a.metals can become magnetic if they have many spinning electrons that create magnetic fields.d.only some metals are attracted by magnets; these metals are called ferromagnetic.

d.wrapping an insulated wire around a metal with ferromagnetic properties and applying an electric current.