In the ring test of $NO_{3}^{-}$ ion,$Fe^{2+}$ ion reduces nitrate ion to nitric oxide,which combines with $Fe^{2+}_{(aq)}$ ion to form a brown complex. Write the reactions involved in the formation of the brown ring.

$NO_{3}^{-} + 3 Fe^{2+} + 4 H^{+} \rightarrow NO + 3 Fe^{3+} + 2 H_{2}O$
$[Fe(H_{2}O)_{6}]^{2+} + NO \rightarrow [Fe(H_{2}O)_{5}(NO)]^{2+} + H_{2}O$
The brown complex formed is $[Fe(H_{2}O)_{5}(NO)]SO_{4}$ (or similar salt depending on the counter ion),which is responsible for the brown ring.