How to go about deciding the acidic strength of a functional group in an aromatic compound? The question requires me to identify the decreasing order of the acidic strength of the following functional group. But I'm afraid I don't know how to distinguish one from the other since all the hydroxyl groups would be in resonance. What would be the next step in this case? I felt like the answer should start with (i) as there is a carbonyl carbon near and the delocalisation would be stabilised.
This question is, at best, flawed. The most acidic protons on the structure provided are not any of the labeled OH protons. Rather, the most acidic position is the one I have drawn a rectangle around below.

Deprotonation at this position produces an anion with a resonance contributor in which both rings are aromatic. The circa 150 kJ/mol resonance stabilization for each ring will vastly outweigh any delocalization that might occur for the oxyanions formed by deprotonating any of the OH groups.