In the passage, the final step given in the procedure is to elute the purified conjugates from the protein G beads by lowering the pH. Thus, given in the question stem that we’d want to avoid damaging proteins and antibodies because of the pH (which has been lowered), we should want to normalize the pH back toward neutral.To me, this question seems to refer as to what would occur AFTER elution. In the passage it describes neutralizing with a basic buffer. I chose B (pH of 7.0) because it had a neutral pH and therefore would not affect the structure of the proteins with the assumption that the neutralization reaction described in the passage had already been done. If that had not been done, then obviously a buffer w/ pH 8.5 would be the most logical answer to neutralize any remaining acid without affecting the structure of the proteins
The passage itself discusses neither basic buffer nor a neutralization reaction. The final step given is the freeing of the conjugates by lowering the pH. From there, as you mentioned, it becomes trivial to choose a slightly basic buffer to neutralize any remaining acid.
Thanks for your question!