I want to compare acidic strength between hydrogen-(a) and hydrogen-(b), I am getting answer as (a) but my classmate and my teacher said that (b) will have more acidic strength. I think (a) should have more acidic strength because it will have more resonance and negative charge will present on oxygen two times
Going by stabilization of conjugate base through resonance, the resonance structures of ($a$) would be:
And the resonance structures of ($b$) would be:
So both ($a$) and ($b$) have two resonance structures, or equivalently, two different ways of placing the negative charge on an oxygen atom.
However, in terms of inductive effects, the carbonyl group ($\ce{C=O}$) acts as an electron-withdrawing group, which means it pulls electron density towards it.
If you look closely, in the resonance structures of ($a$), the carbonyl group is farther away from the negative charge than it is on $\;$($b$).
This means that the two oxygen atoms in ($b$) where resonance takes place in ($b$) can share the negative charge more efficiently than the two oxygen atoms in ($a$) where resonance takes place in $\;\;$($a$).
Therefore, the conjugate base of ($b$) is more stable, and it follows that ($b$) is a stronger acid.
