Answer:
Nalidixic acid
Explanation:
DNA gyrase is present in bacteria that catalyzes the negative super coiling of closed circular DNA. This enzyme belongs to the class of topoisomerase.
Nalidixic acid inhibits the activity of DNA gyrase. This chemical bounds to the A sub unit of the enzyme and prevent the union of the G segment. This causes double strand break in the bacteria DNA.
Thus, the correct answer is option (3).
