(A) → (B) Free H+ions are replaced by Na⊕ which decreases conductance. (B) → (C) Un-dissociated benzoic acid reacts with NaOH and forms salt which increases ions & conductance increases. (C) → (D) After equivalence point at (3), NaOH added further increases Na⊕&OH⊙ ions which further increases the conductance.