JEE Mains Model Paper 4

When freshly prepared solution of FeSO4 is added in a solution containing NO3− ion, it leads to formation of a brown colored complex.
This is known as brown ring test of nitrate
NO3−+3Fe2+ + 4H+ → NO+3Fe3+ + 2HO
[Fe(H2O)6]2+ + NO →

[Fe(H2O)5(NO)]2+

Brown‌ring

+ H2O