Which of the following is not an antacid?

Phenelzine

The answer is 1. Phenelzine.

Phenelzine is an antidepressant, not an antacid. It is a monoamine oxidase inhibitor (MAOI) that is used to treat depression. MAOIs work by increasing the levels of certain neurotransmitters in the brain, such as norepinephrine and dopamine.

Ranitidine, cimetidine, and Al(OH)3 are all antacids. They work by neutralizing stomach acid, which can help to relieve heartburn, acid indigestion, and upset stomach.