The correct answer is (b) apologise.
Word Form Analysis:
— Noun: apology
— Verb: apologise (British English) / apologize (American English)
— Adjective: apologetic
— Adverb: apologetically
Usage: 'I want to apologise for my mistake.'
✗ apological — not a standard English word.
✗ apologify — incorrect; '-ify' suffix is used differently (e.g., beautify, clarify).
✗ enapology — completely incorrect formation.
Note: Both 'apologise' and 'apologize' are correct depending on British/American spelling conventions.
Source: Oxford English Dictionary; Merriam-Webster Dictionary.