In a melt or in solution.
See Also
A compound which, when dissolved in water, barely conducts electrical current can probably be:an ionic salta strong electrolytea strong acida strong basenone of the aboveWhy don't ionic compounds have electrical conductivity as a solid but they do as a liquid? | SocraticWhy are ionic compounds are soluble in water but insoluble in kerosene?Covalent structures - Structures - (CCEA) - GCSE Combined Science Revision - CCEA Double Award - BBC BitesizeExplanation:
In an ionic solid the ions are not free to move and are rigidly held in an electrostatic lattice. If we find a solvent to ionize chemically the ionic lattice (water is a good choice), the ions are now free to move and individual ions are solvated by water molecules, and therefore conduct electricity. Likewise, if you pump enough heat in to melt the lattice (and ionic solids such as common salt have exceptionally high melting points), the ions are now free to move and to carry an electrical current.
