Concept:
This question tests awareness of common suffix patterns (like -ation vs -asion) and double consonant rules in English nouns.
Step 1: Evaluating the incorrect spellings.
• Option A (manifestasion): Words derived from "manifest" use the "-ation" suffix. The correct spelling is manifestation.
• Option B (seerchlight): The root word is "search." The vowel combination is "ea", not "ee." Correct spelling: searchlight.
• Option C (consciousnes): The suffix for state-of-being nouns is "-ness," which requires a double 's'. Correct spelling: consciousness.
Step 2: Confirming the correct choice.
Fundamentalist is spelled correctly. It consists of the root "fundamental" + the suffix "-ist" (denoting a person who adheres to a specific set of principles). Every letter in this word follows standard English orthography.
Final Answer: Option D