p-Aminobenzoic acid (H₂PABA) contains both a carboxylic acid proton and, when protonated, an ammonium proton on the –NH₃⁺ group. When one equivalent of NaOH is added to a solution of H₂PABA, which proton is removed first, and what structural factor makes the corresponding conjugate base more stable? Answer in no more than two sentences.