Step 1: Understanding the Question:
Electrical conductivity requires the presence of mobile charged particles, such as free electrons or free ions.
Step 2: Detailed Explanation:
- Solid sodium chloride (NaCl): It is an ionic compound. In solid state, ions are fixed in a crystal lattice and cannot move. Thus, it does not conduct electricity.
- Aqueous potassium chloride (KCl): When dissolved in water, KCl dissociates into \( K^{+} \) and \( Cl^{-} \) ions which are free to move. It is a good conductor.
- Graphite (s): It has delocalized \( \pi \)-electrons due to its layered structure. These electrons can move, making it a conductor.
- Copper metal (s): Like all metals, it has a "sea of mobile electrons" that facilitates electrical conduction.
Step 3: Final Answer:
Solid sodium chloride is a nonconductor of electricity.