The brown ring test is used for the detection of nitrate (NO3−) or nitrite (NO2−) ions.
In this test, nitric oxide (NO) gas is evolved which reacts with the freshly prepared ferrous sulphate (FeSO4) solution to form a brown ring of nitroso ferrous sulphate.
The gas X is NO.
The reaction is given by:
FeSO4+NO→[Fe(NO)]SO4
The actual composition of the brown ring complex is [Fe(H2O)5(NO)]SO4, which is often represented as [Fe(NO)]SO4.
Thus, X is NO and Y is [Fe(NO)]SO4.
Answer: NO and [Fe(NO)]SO4