Final answer:
Solid ionic compounds are nonconductive because ions are immobile, but they become conductive in solution or when melted.
Step-by-step explanation:
Most solid ionic compounds are electrically nonconductive because the ions are immobile in solids due to the strong ionic bonds holding them together. The strength of these bonds prevents the ions from moving freely in the solid state, resulting in poor conductivity.
However, when ionic compounds are dissolved in water or melted, the ions become free to move. In an aqueous solution or molten state, the ions can carry electric charge and conduct electricity.