A light bluish-green crystalline compound responds to the following tests:
(i). Its aqueous solution gives a brown precipitate on reaction with alkaline `K_2[HgI_4]` solution.
(ii). Its aqueous solution gives a blue colour with `K_3[Fe(CN)_6]` solution.
(iii). Its solution in hydrochloric acid gives a white precipitate with `BaCl_2` solution. Identify the ions present and suggest the formula of the compound.

Explanation

The ions are `NH_(4)^(o+) ,Fe^(2+),SO_(4)^(2-)`
Formula is `(NH_(4))_(2),SO_(4).FeSO_(4).6H_(2)O` (Mohr's salt)