I am burning through some test prep and have a chem question that is troubling me. The questions is as follows:

> How would you compare the acidity of the most acidic proton in each of the following molecules?

1)![enter image description here][1]


2)![enter image description here][2]


3)![enter image description here][3]


  [1]: https://i.sstatic.net/MsgCW.png
  [2]: https://i.sstatic.net/KNvay.png
  [3]: https://i.sstatic.net/Vwwur.png

The answer says 3 is the most acidic, followed by 1, and finally 2 is the least acidic. Can someone please tell me how to determine this? I know the benzene group is electron donating group, but am not quite sure how to correlate this knowledge with determining the relative acidities.