A brown ring is formed in the ring test for `NO_(3)^(-)` ion. It is due to the formation of

Options

A. `[Fe(H_2 O)_5 (NO)]^(2+)`
B. `FeSO_4 . NO_2`
C. `[Fe(H_2 O)_4 (NO)_2]^(2+)`
D. `FeSO_4. HNO_3`

Answer

A

Explanation

When freshly prepared solution of `FeSO_4` is added in a solution containing `NO_3^` ion, it leads to formation of a brown coloured complex. This is known as brown ring test of nitrate.
`NO_3^(-) + 3Fe^(2+) + 4H^+ to NO + 3Fe^(3+) + 2H_2 O`
`[Fe(H_2 O)_6]^(2+) + NO to underset("Brown ring")([Fe(H_2 O)_5 (NO)]^(2+)) + H_2 O`