What is the name of the antibiotic that is widely known and used?

Penicillin is widely recognized as the first antibiotic discovered, revolutionizing the treatment of bacterial infections. Introduced to widespread use in the 1940s, it laid the groundwork for the development of other antibiotics and remains a cornerstone in modern medicine. Its effectiveness against a range of bacterial infections, particularly those caused by gram-positive bacteria, has made it a fundamental part of antimicrobial therapy.

While the other options listed are also important antibiotics, they were developed after penicillin and serve different purposes or target different types of infections. Amoxicillin, for example, is a penicillin derivative that is commonly prescribed, but it is not as historically significant as penicillin itself. Tetracycline and ciprofloxacin are valuable antibiotics as well, each effective against certain strains of bacteria, but they do not carry the same foundational role in antibiotic therapy as penicillin does.