4. The ARIO factors predict $pK_a$ differences:

**A**tom: within a row, electronegativity dominates; within a column, size (polarizability) dominates. - **R**esonance: worth ~10–11 $pK_a$ units per additional delocalization. - **I**nduction: ~2 $pK_a$ units per α-electronegative substituent, falling off rapidly with distance. - **O**rbital (hybri