Which one of the following compounds is a nonelectrolyte when dissolved in water?

The correct answer is C₆H₁₂O₆ (glucose).

Explanation: A nonelectrolyte is a substance that does not dissociate into ions when dissolved in water. Glucose (C₆H₁₂O₆) is a covalent compound and does not ionize in water, making it a nonelectrolyte. On the other hand, the other compounds listed (HCl, CaCl₂, Cu(NO₃)₂, and NaC₂H₃O₂) are all electrolytes because they dissociate into ions when dissolved in water.