A compound A (C2H4O2) reacts with Na metal to form a compound ‘B’ and evolves a gas which burns with a pop sound. Compound ‘A’ on treatment with an alcohol ‘C’ in presence of an acid forms a sweet-smelling compound ‘D’ (C4H8O2). On addition of NaOH to ‘D’ gives back B and C. Identify A, B, C and D write the reactions involved.