Which of the following substances is a strong electrolyte when dissolved in water?

• A. C6H12O6 (glucose)
• B. NaCl
• C. CH3COOH (acetic acid)
• D. NH3 (ammonia)

Answer: (B)

Verified step by step guidance

1. Understand what a strong electrolyte is: a substance that completely dissociates into ions when dissolved in water, allowing the solution to conduct electricity very well.
2. Analyze each substance's behavior in water: glucose (C6H12O6) is a molecular compound that dissolves but does not ionize, so it is a nonelectrolyte.
3. Sodium chloride (NaCl) is an ionic compound that dissociates fully into Na\^{+} and Cl\^{-} ions in water, making it a strong electrolyte.
4. Acetic acid (CH3COOH) is a weak acid that only partially ionizes in water, so it is a weak electrolyte.
5. Ammonia (NH3) is a weak base that partially reacts with water to form NH4\^{+} and OH\^{-}, so it is also a weak electrolyte.