An inorganic Compound 'X' on treatment with concentrated H$$_2$$SO$$_4$$ produces brown fumes and gives dark brown ring with FeSO$$_4$$ in presence of concentrated H$$_2$$SO$$_4$$. Also Compound 'X' gives precipitate 'Y', when its solution in dilute HCl is treated with H$$_2$$S gas. The precipitate 'Y' on treatment with concentrated HNO$$_3$$ followed by excess of NH$$_4$$OH further gives deep blue coloured solution, Compound 'X' is:
