OE


The question stem describes the nucleus as providing major functions for the atom. The missing word will reflect this - that the nucleus is a significant part of an atom. Choice (A)-effulgent (meaning brilliant or radiating) and Choice(E)recondite (meaning confined to and understandable by only an enlightened inner circle)do not fit the scope of the sentence. Choice (C)-epochal (meaning so significant that it brings about a new era), and Choice (F)-evidentiary (meaning important based on evidence) all refer to some aspect of the word "significant", but the connotation of each word is not fitting for the question stem. The correct answers are (B)substantive - meaning important or essential and (D)indispensable- meaning necessary or vital.