Which of the following is an example of an antipyretic?

Aspirin is an example of an antipyretic because it has the ability to reduce fever. It works by inhibiting the production of prostaglandins, which are substances in the body that promote inflammation, pain, and fever. By lowering the levels of these substances, aspirin effectively helps to bring down a high body temperature, making it useful in treating febrile conditions.

In contrast, the other medications listed do not function as antipyretics. Diazepam is primarily a benzodiazepine used for its anxiolytic and muscle relaxant effects, and it does not target fever. Furosemide is a diuretic used to treat fluid retention and hypertension and does not have fever-reducing properties. Phenobarbital is a barbiturate mainly used to control seizures or as a sedative and does not serve the purpose of reducing fever. Thus, aspirin stands out as the correct choice due to its specific action in lowering fever.