Why do ionic crystals conduct electric current in the solid phase liquid phase or when dissolved in water but do not conduct electric current in the solid plase?

Answer 1

In solid state the ions are packed very tightly, so ions are not free to move, therefore no conduction.

Answer 2

Ionic crystals conduct electricity when dissolved in water or in the liquid phase because the ions are free to move and carry electrical charge. In the solid phase, the ions are locked in place and cannot move freely to conduct electricity. In contrast, metals conduct in the solid phase due to the mobility of free electrons within the metallic lattice.