An inorganic compound 'X' on treatment with concentrated H₂SO₄ produces brown fumes and gives dark brown ring with FeSO₄ in presence of concentrated H₂SO₄. Also compound 'X' gives precipitate 'Y', when its solution in dilute HCl is treated with H₂S gas. The precipitate 'Y' on treatment with concentrated HNO₃ followed by excess of NH₄OH further gives deep blue coloured solution, compound 'X' is

Compound ‘X’ is copper nitrate, i.e. $\mathrm{Cu}{\left({\mathrm{NO}}_3\right)}_2$ is an inorganic compound. On treatment with concentrated ${\mathrm{H}}_2{\mathrm{SO}}_4$ produces brown fumes and gives dark brown ring with FeSO₄ in presence of concentrated H₂SO₄. Chemical reaction is as follows

Cu²⁺ is a group II cation with group II reagents

(HCl/H₂S), it gives black coloured precipitates. These precipitates gives blue colour solution on treatment with HNO₃ followed by excess of NH₄OH.