15. An aqueous solution of a compound (A) is acidic towards litmus and (A)
sublimes at about 3000C. (A) on treatment with an excess of NH4SCN gives a red
coloured compound (B) and on treatment with a solution of K4(Fe (CN)6) gives a blue
coloured compound (C). (A) on heating with the excess of K2Cr2O7 in the presence of
concentrated H2SO4 evolves deep red vapour of (D). On passing the vapours of (D)
into a solution of NaOH and d then adding the solution of acetic acid and lead
acetate a yellow precipitate of compound (E) is obtained. Identify A to E and give
chemical equations involved.