JEE Advanced levelSingle correct optionDifficulty 3 of 3el026
Drug D relieves the sneezing of hay fever but does not reduce gastric acid. Drug E lowers gastric acid secretion but does not relieve hay fever. Both act by blocking the actions of the same messenger, histamine. The best conclusion is
AD and E are agonists of the same receptor
BD and E are antagonists at different histamine receptor subtypes, and their selectivity comes from different binding-site shapes
CD and E inhibit the enzyme that makes histamine
Dhistamine has one receptor only, so one observation must be wrong
Answer: B
Blocking the same messenger but with different outcomes means different receptors were blocked. Each drug fits one subtype only because the binding-site shapes differ. This is receptor selectivity, and both are antagonists.