Final answer:
Ritalin is classified as a Schedule II controlled substance in the United States, indicating it has accepted medical use but also a high potential for abuse and dependence.
Step-by-step explanation:
Ritalin, also known by its generic name methylphenidate, is classified as a Schedule II controlled substance in the United States. This classification indicates that while Ritalin has a medically accepted use, it also has a high potential for abuse, which may lead to severe psychological or physical dependence. Therefore, the correct answer to the question is b. I, as Schedule II substances are denoted with the Roman numeral II.