Chemistry - GOC Question with Solution | TestHub

Removing H₁ puts the negative charge on the nitrogen attached to the ring :

Removing H₂ puts the negative charge on the benzylic nitrogen :

The anion on the ring nitrogen is delocalised into the aromatic ring by resonance, while the charge on the benzylic nitrogen is localised. Delocalisation makes the first conjugate base more stable, so the aryl N-H proton H₁ is more acidic.