An organic compound (A) (C6H6O) gives a characteristic colour with aq.FeCl3 solution. When CO2 gas is passed through an alkaline solution of A at 400 K under pressure, compound (B) is obtained. Compound B on acidification gives (C) which reacts with acetylchloride to form (D) which is a popular pain killer. Deduce the structure of A,B, C and D.
