An inorganic compound 'X' on treatment with concentrated H₂SO₄ produces brown fumes and given 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 given deep blue coloured solution, Compound 'X' is:

$X\underset{H_{2}S{O}_4}{\overset{Conc}{\to }}$ Brown fumes + Brown ring test with FeSO₄/H₂SO₄

$x\underset{HCl}{\overset{H_{2}S}{\to }}Y\left(ppt\right)\underset{HN{O}_3}{\overset{Conc}{\to }}dissolved\underset{N{H}_{4}OH}{\overset{}{\to }}$ Deep blue colour solution

In cation analysis of Cu⁺ ions, precipitate formed is CuS on treating with H₂S and HCl which dissolved in HNO₃ and produced blue colour complex solution ${\left[Cu{\left(N{H}_3\right)}_4\right]}^{++}$ in NH₄OH. Brown fumes and brown ring performance given by nitrate