Ionic solids conduct electricity in molten state but not in solid state. Explain.

Hint: Ionic solids consist of oppositely charged ions arranged in space with a strong electrostatic force existing in between them. The arrangement of cations and anions arranged in a geometrical pattern gives them a crystalline appearance at room temperature.

Complete step by step answer:
Since, Ionic solids consist of oppositely charged ions (cations and anions) arranged with a strong electrostatic force of attraction between them (Ionic bonds), which constitutes in a geometrical arrangement and gives them a crystalline appearance at room temperature or standard temperature and pressure, And since because of the electrostatic force acting between the ions, every anion is surrounded by many cations and similarly every cation in turn is surrounded by anions, which results in the strong bonding structure of ionic solids.
Thus, resulting in high melting points ("high" generally as these are higher than metallic but lower than covalent) as well as high dielectric constants, most of the ionic solids are electrically insulating in their solid state as the ions are fixed at its position and are entrapped in the crystal lattice and cannot move when the electric field is applied, while they become mobile as soon as they melt, as the arrangement of ions in the solids is destroyed and the mobility of the ions corresponds to their conducting ability whenever an electric field is applied. For example:- NaCl.

Note: One can get confused with the exceptional case when this effect is observed in ionic solids if defects occur in their crystalline lattices which allow them to conduct even in their solid states.