In a similar experiment, unlabeled 4-butanolide was allowed to stand in an acidic solution in which the

Question:

In a similar experiment, unlabeled 4-butanolide was allowed to stand in an acidic solution in which the water had been labeled with 18O. When the lactone was extracted from the solution after 4 days, it was found to contain 18O. Which oxygen of the lactone do you think became isotopically labeled?