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