Chemistry - GOC Question with Solution | TestHub

Removing ${\mathrm{H}}_1$ puts the negative charge on the $-\mathrm{N}{\mathrm{H}}_2$ nitrogen :

Removing ${\mathrm{H}}_2$ puts the negative charge on the $-\mathrm{NHC}{\mathrm{H}}_3$ nitrogen :

In both cases the charge is on nitrogen with no resonance, so compare induction : the methyl group donates electron density and destabilises the second anion. The first conjugate base is more stable, so the N-H proton of the $-\mathrm{N}{\mathrm{H}}_2$ group, ${\mathrm{H}}_1$, is more acidic.