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${\mathrm{NO}}_2^{-}$ ion can be detected by brown ring test in presence of ${\mathrm{NO}}_3^{-}$ ion. both ${\mathrm{NO}}_2^{-}$and ${\mathrm{NO}}_3^{-}$ ions are confirmed by brown ring test. because brown ring test is performed, by adding Iron (II) sulphate to a solution of a nitrate. Then slowly adding concentrated H2​SO4​ such that the acid forms a layer below the aqueous solution.