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

• A. NaCl
• B. C_6H_{12}O_6 (glucose)
• C. CCl_4
• D. CH_3OH (methanol)

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. Identify the nature of each substance given: NaCl is an ionic compound, glucose (C_6H_{12}O_6) is a molecular compound (a sugar), CCl_4 is a nonpolar molecular compound, and CH_3OH (methanol) is a polar molecular compound.
3. Recall that ionic compounds like NaCl dissociate fully into Na^+ and Cl^- ions in water, making them strong electrolytes.
4. Recognize that molecular compounds such as glucose and methanol dissolve as whole molecules without producing ions, so they are nonelectrolytes or weak electrolytes.
5. Conclude that among the options, NaCl is the strong electrolyte because it dissociates completely into ions in aqueous solution.