Question

The pair in which both the species have the same magnetic moment (spin only) is :

• A. ${\left[Mn{\left(H_{2}O\right)}_6\right]}^{2+}$ and ${\left[Cr\left(H_{2}O\right)\right]}^{2+}$
• B. ${\left[Cr{\left(H_{2}O\right)}_6\right]}^{2+}$ and ${\left[CoC{l}_4\right]}^{2-}$
• C. ${\left[Cr{\left(H_{2}O\right)}_6\right]}^{2+}$ and ${\left[Fe{\left(H_{2}O\right)}_6\right]}^{2+}$
• D. ${\left[Co(OH{)}_4\right]}^{2-}$ and ${\left[Fe{\left(N{H}_3\right)}_6\right]}^{2+}$

Answer 1

Answer: (C)

Complex	$e^{-}$ configuration	no. of unpaired $e^{-}$
$[Mn(H_{2}O{)}_6{]}^{2+}$ WFL		5
$[Cr(H_{2}O{)}_6{]}^{2+}$ WFL		4
$[COC{l}_4{]}^{2-}$ Tetrahedral		3
$[Fe(H_{2}O{)}_6{]}^{2+}$ WFL		4
$[Co(OH{)}_4{]}^{2-}$ WFL		3
Tetrahedral $[Fe(N{H}_3{)}_6{]}^{2+}$		4

Thus complex ${\left[Cr{\left(H_{2}O\right)}_6\right]}^{2+}$ and ${\left[Fe{\left(H_{2}O\right)}_6\right]}^{2+}$ have same no. of unpaired $e^{-}$ and hence same magnetic moment (spin only).