Final answer:
The student may have lost THF during their refluxing procedure through evaporation.
Step-by-step explanation:
The student may have lost THF during their refluxing procedure through evaporation. Evaporation is the process by which a liquid turns into a gas when heated, and THF (tetrahydrofuran) is a volatile liquid that easily evaporates at room temperature. During refluxing, which involves continuous boiling, THF can escape from the reaction flask as vapor and be lost.