Question

The complex $\left[Fe\right(H_{2}O{)}_{5}NO{]}^{2+}$ is formed in the brown ring test for nitrates when freshly prepared $FeS{O}_4$ solution is added to aqueous solution of $N{O}_3^{-}$ followed by addition of $conc.H_{2}S{O}_4$. Select correct statement about this complex.

• A. Colour change is due to charge transfer.
• B. It has iron in +1 oxidate state and nitrosyl as $N{O}^{+}$.
• C. It has magnetic moment of 3.87 BM confirming three unpaired electrons of Fe.
• D. All of the above statements are correct.

Answer 1

The correct option is D All of the above statements are correct.

$\left[Fe\right(H_{2}O{)}_{5}NO{]}^{2+}$- Fe is in +1 oxidation state as nitrosyl is $N{O}^{+}$. The brown colour appears due to charge transfer.
$F{e}^{+}$ electronic configuration is $\left[Ar\right]3d^{5}4s^1$. Electron in 4s now pushed to 3d orbital leading to 3 unpaired electrons and hence, magnetic moment of 3.87 BM.