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NEET levelSingle correct optionDifficulty 1 of 3pn168

The brown ring formed at the junction of the two layers in the brown ring test for nitrate is due to the complex

A $[Fe (CN) X_{6}] X^{4 -}$
B $[Fe (H X_{2} O) X_{6}] X^{3 +}$
C $[Cu (NH X_{3}) X_{4}] X^{2 +}$
D $[Fe (H X_{2} O) X_{5} NO] X^{2 +}$

Answer: D

Nitrate is reduced to

NO

by

Fe X^{2 +}

in acid, and

NO

then binds to

[Fe (H X_{2} O) X_{6}] X^{2 +}

to give the brown

[Fe (H X_{2} O) X_{5} NO] X^{2 +}

at the interface with conc.

H X_{2} SO X_{4}

.

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