A brown ring is formed in the ring test for NO3

– ion. It is due to the formation of


When freshly prepared solution of FeSO4 is added in the solution containing NO3 ion. It leads to the formation of brown coloured complex. This is known as brown colour test of nitrate.


+ 3Fe2+ + 4H+ NO + 3Fe3+ + 2H2O


[Fe(H2O6)]2+ + NO [Fe(H2O)5 (NO)]2+ + H2O


Hence the correct option is (i).

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