Ace the Brainy Challenge with CAT4 2025 – Unleash Your Cognitive Superpowers!

The correct response highlights the concept of "lexicon," which refers to the entire collection of words and phrases a person knows and uses. When Ron looks up unfamiliar words, he is actively working to enlarge his own lexicon by adding new vocabulary to his repertoire. This process of encountering and learning new words helps to deepen his understanding and mastery of language.

While options like semantic vocabulary relate to the meanings of words and their relationships, and synonymous vocabulary involves words with similar meanings, they do not directly capture the notion of expanding one's overall collection of words. Colloquial vocabulary pertains to informal language and slang, which isn't necessarily linked to looking up unknown words to expand formal or academic language. By choosing to look up words he does not know, Ron is effectively enhancing his lexicon with a broader range of vocabulary.