Brown ring test for nitrate

1. A.
   A dark brown ring is formed at the junction of two solutions.
2. B.
   Ring is formed due to nitroferrous sulphate complex.
3. C.
   The brown complex is $\left\lbrack Fe\left( H_{2}O \right)_{5}(NO) \right\rbrack{SO}_{4}$.
4. D.
   Heating the nitrate salt with conc. $H_{2}{SO}_{4}$, light brown fumes are evolved.

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