Penicillin was discovered by:

The correct answer is Option (4) → Alexander Fleming

Penicillin was the first antibiotic to be discovered, and it was a chance discovery. Alexander Fleming was working on Staphylococci bacteria. He saw a mould growing in one of his unwashed culture plates, and the bacteria could not grow around it. He found that this was due to a chemical made by the mould, Penicillium notatum, and named it penicillin.

(4) Alexander Fleming — Correct. Fleming discovered penicillin by chance and named the chemical made by the mould penicillin. Its full potential as an effective antibiotic was established much later by Ernst Chain and Howard Florey.

NCERT Extract:
Antibiotics – …