Which of these drugs is considered a narcotic and falls under Schedule II?

Opium is classified as a narcotic and falls under Schedule II due to its high potential for abuse and the possibility of severe psychological or physical dependence. This classification is based on the Drug Enforcement Administration (DEA) regulations that categorize substances based on their medical use, potential for abuse, and safety or dependence liability. Opium, derived from the opium poppy plant, has a long history of use in pain relief, but it is also associated with addiction and other risks, warranting its Schedule II classification.

In contrast, the other options listed are not classified as narcotics or do not fall under Schedule II. Diazepam is a benzodiazepine and is classified under Schedule IV, which indicates a lower potential for abuse. Metformin is an antihyperglycemic medication used to manage diabetes and does not have abuse potential, while omeprazole is a proton pump inhibitor used to treat conditions related to excess stomach acid and also does not have narcotic properties or a potential for abuse. Thus, opium is the only drug from the given choices that meets the criteria for being a narcotic and classified under Schedule II.