Question

The pair having the same magnetic moment is [atomic number, $Cr=24,Mn=25,Fe=26$ and $Co=27]$

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

Answer 1

Answer: (D)

The complexes, in which metals ions have same number of unpaired electrons will have same magnetic moment.

Complex ion	Electronic configuration of metal ion	Number of unpaired electrons $(n)$
${\left[Cr{\left(H_{2}O\right)}_6\right]}^{2+}$	$C{r}^{2+};[Ar]3d^4$
${\left[Fe{\left(H_{2}O\right)}_6\right]}^{2+}$	$F{e}^{2+};[Ar]3d^6$
${\left[Mn{\left(H_{2}O\right)}_6\right]}^{2+}$	$M{n}^{2+};[Ar]3d^5$
${\left[CoC{l}_4\right]}^{2-}$	$C{o}^{2+};[Ar]3d^7$