Chemistry - GOC Question with Solution | TestHub

Removing Ha gives a carbanion allylic to the central C=C bond, and that double bond is conjugated with both carbonyl groups : the charge delocalises through the diene system onto BOTH carbonyl oxygens (a vinylogous enolate with four resonance structures). Hb and Hc are ordinary α protons whose anions delocalise over only one carbonyl, and Hd is a plain beta C-H with no resonance stabilisation at all. The most stabilised conjugate base comes from Ha, so Ha is the most acidic.