Final answer:
Elizabeth's conversation with Mr. Collins backfires when he invites her to the Netherfield ball as his date, causing her discomfort due to his unwelcome affections.
Step-by-step explanation:
Elizabeth's conversation with Mr. Collins about the Netherfield ball backfires because Mr. Collins invites her to the ball as his date (Option C). This is not an outcome she desires, as Mr. Collins's affections towards her are unwelcome.
The discussion is strained and features Mr. Collins's stiff behavior and Elizabeth's discomfort.
His proposal to her is an awkward moment that amplifies Elizabeth's unfavorable feelings towards him, yet his actions show an increased determination to pursue her, the opposite of her hopes for a decline in his interest.