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.

Explanation

As `1%` Solution of (A) in presence violet colouration with white portion of egg (Biuret test) and (A) with potassium iodide gives brown precipitate which turned white on adding hypo. The (A) may be anhydrous `CUSO_(4)` (White). This is further confirmed by the reaction of (A) with potassium cyanide.
`2CuSO_(4)+4KI` to `Cu_(2)I_(2)uparrow("yellow or brown")+2K_(2)sO_(4)`
(A),(B)
`I_(2)+2Na_(2)S_(2)O_(3)` to `Na_(2)S_(4)O_(6)+2NaI`
`2CuSO_(4)+4KCN to 2CU(CN))_(2)downarrow("yellow")+2K_(2)SO_(4),2CU(CN)_(2)to2CuCNdownarrow("White")+(CN)_(2)uparrow`
`2CuCN+6KCN to 2K_(3)[Cu(CN)_(4)]` (Colourless soluble complex).