Which type of substance can conduct electricity in the liquid phase but not in the solid phase?
(1) ionic compound
(2) molecular compound
(3) metallic element
(4) nonmetallic element

Ionic compound, this is because the ions in a compound consist of a metal and a nonmetal... Or cation and anion. This means that they have opposite charges, so when they are in liquid form they allow for movement of electrify because they are free flowing. In contrast, as a solid they are tightly attracted and compacted so a charge cannot be carried through. Hope that helps!