(i) An aqueous solution of a white coloured compound `(A)` on reaction with `HCl` gives a white precipitate of compound `(B)`.
(ii) `(B)` becomes soluble in chlorine water with the formation of `(C)`
(iii) `(C)` reacts with `KI` to give a precipitate which becomes solube in excess of it forming a compount `(D)`. the compound `(D)` is used for detecting ammonium salts.
(iv) `(B)` and `(C)` both, on treatement with `SnCl_(2)` give a grey precipitate of `(E)`.
(v) When conc. `H_(2)SO_(4)` is added slowly into a mixture of cold solutions of `(A)` and `FeSO_(4)` is added slowly into a mixture of cold solutions of `(A)` and `FeSO_(4)`, a brown ring of compound `(F)` is formed.
(A) on dissociation in `H_(2)SO_(4)` gives:

Options

A. `Hg_(2)SO_(4)`
B. `HgSO_(4)`
C. `HgHSO_(4)`
D. `FeSO_(4)`