Anhydrous white solid `(A)` on addition of potassium iodine solution gave a brown precipitate which turned white `(B)` on addition of excees of hypo solution. When potasium cyanide is added to an aqeous Solution of `(A)`a white precipitate is formed which then dissolved in excess forming `(C )` A Solution `(%)` of `(A)` on adding to a solution of white portion of egg produced violet colouration in alkaline medium `(i.e)` in presence of `NaOH)` identify compound `(A)` and explain the reactions.