Final answer:
The correct word to complete the quote is umbrage, which means offense or resentment.
Step-by-step explanation:
The correct vocabulary word to complete the quote from To Kill a Mockingbird is umbrage.
Umbrage means offense or resentment. In the context of the quote, the narrator is unsure of what Jem resented the most, but he took offense at Mrs. Dubose's assessment of the family's mental hygiene. This implies that Mrs. Dubose made a negative judgment about the family's mental well-being, and the narrator felt offended by her statement.