Question

Cold ferrous sulphate solution on absorption of $NO$ develops brown colour due to the formation of

• A. paramagnetic $[Fe(H_2O)_5(NO)]SO_4$
• B. diamagnetic $[Fe(H_2O)_5(N_3)]SO_4$
• C. paramagnetic $[Fe(H_2O)_5(NO_3)](SO_4)_2$
• D. diamagnetic $[Fe(H_2O)_4(SO_4)]NO_3$

Answer 1

Answer: (A)

paramagnetic $[Fe(H_2O)_5(NO)]SO_4$

Answer 2

Cold $FeSO _{4}$ solution on absorption of NO develops brown colour due to the formation of $\left[ Fe \left( H _{2} O \right)_{5}( NO )\right] SO _{4}$.
$FeSO _{4}+ NO +5 H _{2} O \longrightarrow \underset{\text{Brown ring complex}}{\left[ Fe \left( H _{2} O \right)_{5}( NO )\right] SO _{4}}$
This complex has $3.89\, BM$ magnetic moment shows that it has 3 unpaired electrons.