Final answer:
The sentence that shows Mrs. Bennet as rationally minded is when she stresses the importance of Mr. Bennet visiting Mr. Bingley to facilitate future social interactions.
Step-by-step explanation:
The sentence from the Pride and Prejudice excerpt that best supports the idea that Mrs. Bennet is gossipy yet rationally minded is “Indeed you must go, for it will be impossible for us to visit him if you do not.” This sentence demonstrates Mrs. Bennet's awareness of social norms and the practical implications of visiting Mr. Bingley. Her emphasis on the necessity of Mr. Bennet's visit to enable the family's social acquaintance with Mr. Bingley shows rational planning behind her social maneuverings.