Which of the following is an example of an antibiotic?

Amoxicillin is an antibiotic that belongs to the penicillin class of medications. It is specifically designed to fight bacterial infections by inhibiting the growth of bacteria. Antibiotics work by targeting organisms that cause infections, effectively treating conditions such as strep throat, pneumonia, and other bacterial diseases.

In the context of the other options, acetaminophen is an analgesic and antipyretic medication used to relieve pain and reduce fever but does not have antibacterial properties. Ibuprofen is a nonsteroidal anti-inflammatory drug (NSAID) that is primarily used for pain relief, inflammation reduction, and fever reduction, similarly lacking the ability to combat bacterial infections. Diphenhydramine is an antihistamine used to relieve symptoms of allergies, motion sickness, and insomnia, and it also does not target bacteria.

Hence, among the choices, amoxicillin is the only medication designated to treat bacterial infections, classifying it as an antibiotic.