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

• A. NaCl
• B. C_6H_{12}O_6 (glucose)
• C. CH_3COOH (acetic acid)
• D. NH_3 (ammonia)

Answer: (A)

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. Examine each substance's behavior in water: NaCl is an ionic compound that dissociates fully into Na\^+ and Cl\^- ions, making it a strong electrolyte.
3. C_6H_{12}O_6 (glucose) is a molecular compound that dissolves but does not ionize significantly, so it is a nonelectrolyte or very weak electrolyte.
4. CH_3COOH (acetic acid) is a weak acid that partially ionizes in water, so it is a weak electrolyte, not a strong one.
5. NH_3 (ammonia) is a weak base that partially reacts with water to form NH_4\^+ and OH\^- ions, but this ionization is incomplete, so it is also a weak electrolyte.