Hey Madison,
So far, it looks like you understood everything in the correct way. I think that maybe the confusion is because of the molecule that is being stabilized. Question 49 is stabilizing pantothenate, which in the last paragraph of the passage, states that it is stabilized by carboxylate, which was why Q49 answer was C. Ionic interactions in Q50 is stabilized by the positive charged AAs which interacts with the negatively charged ADPs, like you said.
Hope that was helpful. Let me know if you have any more questions.
Cheers,
Molly