Step 1: Know what Indomethacin is.
Indomethacin is a classic NSAID used for anti-inflammatory and analgesic purposes. It is one of the most potent COX inhibitors available. To classify it correctly, we look at its chemical structure.
Step 2: Understand the NSAID chemical classes.
NSAIDs are broadly grouped by their acidic functional group and ring system: Aryl/Heteroaryl acetic acids (e.g., diclofenac), Aryl/Heteroaryl propionic acids (e.g., ibuprofen), Indole-3-acetic acid derivatives, N-aryl anthranilic acids (fenamates), and Enolic acids (oxicams).
Step 3: Identify Indomethacin's ring system.
Indomethacin contains an indole ring (a bicyclic system with a benzene fused to a pyrrole). The acetic acid side chain is at position 3 of the indole ring. This places it firmly in the Indole-3-acetic acid category.
Step 4: Rule out the distractors.
Aryl/Heteroaryl acetic acid (Option 1) includes drugs like diclofenac that have a simple aryl ring, not a fused indole. Aryl propionic acids (Option 2) include ibuprofen and naproxen, which have a propionic (3-carbon) acid, whereas indomethacin has an acetic (2-carbon) acid. N-aryl anthranilic acid (Option 4) describes mefenamic acid.
Step 5: Confirm the answer.
Indomethacin = indole ring + acetic acid at position 3 = Indole-3-acetic acid class. This is the textbook classification.
Answer: Option (3) — Indole-3 acetic acid