Which of the following substances is considered a notable in Schedule III?

Nalorphine is classified as a notable substance in Schedule III due to its specific properties as a narcotic antagonist. It is an older drug that can be used to counteract the effects of opioid overdose, which distinguishes it from many other substances in this schedule that are primarily analgesics. Schedule III drugs are recognized for their potential for abuse but less than those in Schedules I and II. Nalorphine's unique role in the opioid spectrum and its acceptance for medical use without the higher restrictions of the more dangerous schedules make it a notable entry in Schedule III.

In contrast, substances like chlordiazepoxide and dihydrocodeine, while they may also be in Schedule III, are recognized primarily for their sedative and analgesic properties, respectively, rather than unique pharmacological actions. Morphine, on the other hand, is classified as a Schedule II substance due to its high potential for abuse and strong dependency issues. Thus, nalorphine's specific use and classification as a notable agent in managing opioid-related conditions reinforce its position within Schedule III.