Comparison Note — Acid-Base Theories — Notes

Feature	Arrhenius	Bronsted-Lowry	Lewis
Acid defined as	Produces $H^{+}$ in water	Proton ( $H^{+}$ ) donor	Electron pair acceptor
Base defined as	Produces $OH^{-}$ in water	Proton ( $H^{+}$ ) acceptor	Electron pair donor
Medium required	Aqueous only	Any solvent	Any medium (no solvent needed)
Explains $BF_{3}$ + $NH_{3}$ ?	No	No (no proton transfer)	Yes — $BF_{3}$ accepts $e^{-}$ pair from $NH_{3}$
Explains $NH_{3}$ + HCl?	Partially	Yes — $NH_{3}$ accepts $H^{+}$	Yes
Conjugate pairs?	Not defined	Yes (HA / $A^{-}$ ; B $H^{+}$ / B)	Not applicable
Scope	Narrowest	Intermediate	Broadest
NEET frequency	Low (definition Qs)	High (conjugate pair, Ka × Kb)	Moderate (Lewis acid examples)
Key limitation	Only aqueous; cannot explain $NH_{3}$ as base without $OH^{-}$	Cannot explain non-proton transfer acid-base (e.g., $CO_{2}$ + CaO)	So broad that even simple cation-anion interactions qualify
Example acids	HCl, $H_{2}SO_{4}$	HCl, $H_{2}O$ (as acid)	$BF_{3}$ , $AlCl_{3}$ , $Fe^{3+}$
Example bases	NaOH, KOH	$NH_{3}$ , $H_{2}O$ (as base)	$NH_{3}$ , $F^{-}$ , $OH^{-}$

Key NEET fact: Ka × Kb = Kw = 10^{-14} at 25°C for any conjugate acid-base pair (Bronsted-Lowry framework).