12. Which one of the following substances does not exist in the indicated solid type? A.graphite–covalent…

12. Which one of the following substances does not exist in the
indicated solid type? A.graphite–covalent crystals B.Na–metallic
crystals C.SiO2–molecular crystals D.NaCl–ionic crystals
E.diamond–covalent crystal    (Please explain how to do
this sort of problem)