Which of the following substances would be the best electrical insulator?

• A. Sodium chloride (NaCl) in aqueous solution
• B. Copper (Cu)
• C. Graphite (C)
• D. Diamond (C)

Answer: (D)

Verified step by step guidance

1. Understand that electrical conductivity depends on the availability of free charge carriers (such as electrons or ions) that can move through the substance.
2. Analyze each substance: Sodium chloride (NaCl) in aqueous solution dissociates into ions, making it a good conductor of electricity in solution.
3. Copper (Cu) is a metal with free electrons that move easily, making it an excellent electrical conductor.
4. Graphite (C) has a layered structure with delocalized electrons within the layers, allowing it to conduct electricity well along the planes.
5. Diamond (C), unlike graphite, has a rigid three-dimensional covalent network with no free electrons or ions, making it an excellent electrical insulator.