Question

What are acidic hydrogens?

Answer 1

See below

Explanation:

'acidic hydrogen means, it has tendency to be released as H+ ion . So, if any H-atom is attached to another atom or group of atoms with higher electronegativity, that H-atom is a potential acidic H-atom.
It should be keep in mind that no acid is actually acid unless it meets suitable base, in other words acidity or basicity are the comparative words.
There are many other reason to be a acidic hydrogen... Example:- electromeric effect , inductive effect , resonance effect,hyperconjugation etc