Answer
B.
Work Step by Step
A. is incorrect since the proton gradient has a low pH in the lumen and a higher pH in the stroma, to which protons return via the ATP Synthase. C. is wrong because the cytoplasm is unaffected, in terms of its pH, by photosynthesis, and D. can be eliminated since the antenna complex is in the hydrophobic thylakoid membrane where pH is irrelevant due to the lack of water.
