Which of the following is used as antacid?

Zantac

The answer is 3. Zantac.

Zantac is a brand name for ranitidine, which is an H2 receptor antagonist. H2 receptor antagonists work by blocking the production of stomach acid. This helps to relieve heartburn, acid indigestion, and upset stomach.

Iproniazid, salvarsan, and chloramphenicol are not used as antacids.

Iproniazid is an antidepressant that is no longer used due to its risk of liver damage.

Salvarsan is an arsenic-containing drug that was used to treat syphilis in the early 20th century. It is no longer used due to its toxicity.

Chloramphenicol is an antibiotic that is used to treat a variety of infections. It is not used as an antacid.