Insects often get stuck in the sap of ancient trees. The sap along with the insect inside harden forming a fossil. What kind of fossil is this? Cast
Crystallization
Mold
Trace

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.