Chemistry - GOC Question with Solution | TestHub

Removing ${\mathrm{H}}_1$ gives the central carbanion :

Removing ${\mathrm{H}}_2$ gives the α carbanion :

Both charges are on carbon, so compare resonance : the first anion is flanked by two carbonyls and the charge is delocalised over two oxygens, while the second is delocalised over only one carbonyl. More delocalisation means a more stable conjugate base, so the central proton ${\mathrm{H}}_1$ is more acidic.