Topic: Interchange of Parts of Speech,

Best Answer Explained in Below-:

The noun form of "brief" is "brevity," making option C the correct choice. The word "brief" is an adjective that describes something that is short in duration or extent. To express the quality or state of being brief, the English language uses the term "brevity." This noun encapsulates the essence of something being condensed, succinct, or lasting for a very short time.

Option A, "short," is also an adjective, not a noun, thus excluding it from being the correct answer. Option B, "brefness," is a misspelling; the correct term is "brevity." Lastly, option D, "briefable," is an adjective that refers to something that can be made brief, therefore not fitting as a noun.

Understanding the distinction between nouns and adjectives is crucial in identifying the correct answer. Nouns typically denote a person, place, thing, or idea, whereas adjectives describe or modify nouns. Hence, "brevity" as a noun directly relates to the quality expressed by the adjective "brief," solidifying its status as the correct answer.