Which of the following is not an antacid?

Step-by-step solution

Antacids are substances that neutralize excess stomach acid to relieve heartburn and indigestion. Common examples include aluminium hydroxide, magnesium hydroxide, cimetidine, and ranitidine. Cimetidine and ranitidine are H₂ -receptor antagonists that reduce acid production in the stomach, and they are widely used as antacids. Aluminium hydroxide is a common inorganic antacid used to neutralize gastric acid. Phenelzine is a monoamine oxidase inhibitor (MAOI) used as an antidepressant, not as an antacid. Answer: Phe