* Solid NaCl: Non-conductor

* Explanation: In solid NaCl, the sodium (Na+) and chloride (Cl-) ions are held tightly in a crystal lattice. They are not free to move, and therefore cannot carry an electrical current.

* Molten NaCl: Conductor

* Explanation: When NaCl is melted, the ionic bonds break, and the ions become free to move. These mobile ions can carry an electric current when a voltage is applied, making molten NaCl a good conductor.

* Aqueous solution of NaCl: Conductor

* Explanation: When NaCl dissolves in water, it dissociates into Na+ and Cl- ions. These ions are surrounded by water molecules and can move freely throughout the solution. This mobility allows the solution to conduct electricity.

In summary:

* The key to electrical conductivity in ionic compounds is the mobility of ions.

* Solid NaCl has ions in a fixed lattice, so it doesn't conduct.

* Molten NaCl and aqueous NaCl have free-moving ions, making them good conductors.