The sodium salt of a carboxylic acid `(A)` was produced by passing a gas `(B)` into an aqueous solution of caustic alkali at an envolved temperature and pressure `(A)` on heating in the presence of sodium hydroxide followed by the treatment with sulphuric acid gave a dibasic acid `(C)`. A sample of `0.4 gm` of acid `(C)` on combustion gave `0.08 gm` of water,`.39gm` of `CO_2` and weighting `1.0 gm` on ignition yielded `0.71 gm` of silver as residue. Identify `(A), (B),` and (C)`.

Explanation

(A) HCOOH (B) CO (C) COO H.COOH