Identify the INCORRECTLY spelt word in the given sentence. He introduced…

Concept: Several everyday English adjectives are spelled with the letter sequence "-ble" at the end — as in feeble, noble, capable, and terrible. This fixed spelling is a frequent target for an exam spelling trap called metathesis: the last two letters of the word are transposed, turning the standard "-ble" ending into a "-bel" ending that looks plausible but is not a standard English spelling.

Application: Checking every word in the sentence against standard spelling: "introduced", "valiant", and "opponent" each follow a regular English spelling pattern, while the word spelt "feebel" breaks the "-ble" pattern shared by feeble, noble, and capable — the final two letters have been transposed, so the standard spelling is "feeble".

Contrast:

• Introduced — correctly spells the past tense of "introduce" by adding "-d" to a verb that already ends in a silent "e" (introduce → introduced, produce → produced).

• Valiant — ends in the standard English adjective sequence "-iant", the same ending as in "brilliant" and "defiant".

• Opponent — correctly doubles the "p" where the Latin prefix "ob-" assimilates to "op-" before a root beginning with "p", the same pattern as "oppose" and "opposite".

Result: The incorrectly spelt word in the sentence is "feebel"; the standard spelling is "feeble".