As heat is added to a substance undergoing a phase change, the temperature remains constant because the energy is being used to break covalent bonds lower the specific heat capacity overcome intermolecular forces oppose electron cloud repulsions

you need to have a picture of the atom that way we can answer it

ca has a crystalline lattice with positive ions (since it is a metal, metals are positively charged) and electrons flow freely in its structure since the ca atoms have a large nuclear radius so the electrons are not tightly held, therefore the electrons can flow freely since they are not being highly attracted by the nucleus. moreover, one of the properties of metals are that they are conductors of electricity, thus proving ca is the element.