Sodium phenoxide when heated with CO₂ under pressure at 125^oC yields a product which on acetylation produces C.

The major product C would be

     O⁻Na⁺  ⇌  O⁻ + Na⁺
      |             |
 Benzene ring    Benzene ring

Resonance structures:
Benzene–O⁻ ⇌ Benzene–C=O⁻

Reaction steps:

Benzene–C=O + CO₂ → Intermediate (carboxylation)

Products:

(C) OCOCH₃
|
Benzene–COOH

(B) OH
|
Benzene–COOH

Further:
(Benzene–OH–COOH) ⇌ Benzene–OH–COO⁻ (in presence of H⁺)

Acetylation:
(B) + (CH₃CO)₂O → (C)