Which one of the following chemicals is responsible for the production of HCl in the stomach leading to irritation and pain?

Solution

Chemistry ma’am · 3 steps

Spot the imidazole ring with an ethylamine chain: that is histamine, the trigger for stomach acid.

1. How acid is made. Histamine binds to H₂ receptors in the stomach wall and makes it release pepsin and HCl. Too much acid causes irritation, pain and, over time, ulcers.
2. Identify each structure. Find the main ring and the side chain in each option. Then match the structure to its everyday role.

   Option	Structure clue	Compound	Role in the body or as a drug
   (a)	Benzene fused to a ring with C=O, NH and SO₂	Saccharin	Artificial sweetener
   (b)	Imidazole ring with a -CH₂CH₂NH₂ chain	Histamine	Stimulates HCl secretion in the stomach
   (c)	Indole-type ring with an OH and an aminoethyl chain	Serotonin skeleton	Neurotransmitter linked to mood
   (d)	Phenylethyl group on a hydrazine, -NHNH₂	Phenelzine	Antidepressant (tranquilizer)

3. So. The compound behind stomach acid, irritation and pain is histamine, option (b). Antacids such as cimetidine and ranitidine work because they stop histamine from binding at the H₂ receptor.

The idea to keep. Imidazole ring plus an ethylamine chain means histamine. It drives HCl secretion, and drugs like cimetidine and ranitidine cut acid by stopping histamine from binding.

Answer from the NTA final answer key. Solution by PrepWiser.