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

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

Answer: (C)

Verified step by step guidance

1. Understand what an electrolyte is: an electrolyte is a substance that dissociates into ions when dissolved in water, allowing the solution to conduct electricity.
2. Examine each substance's nature and behavior in water: CH_3OH (methanol) and C_6H_{12}O_6 (glucose) are molecular compounds that dissolve but do not ionize significantly, so they are nonelectrolytes.
3. Consider NaCl: it is an ionic compound that dissociates completely into Na^+ and Cl^- ions in water, making the solution conductive and thus an electrolyte.
4. Look at CCl_4 (carbon tetrachloride): it is a nonpolar molecular compound that does not dissolve well in water and does not produce ions, so it is not an electrolyte.
5. Conclude that among the given substances, only NaCl acts as an electrolyte because it produces ions in aqueous solution.