The $d$ electron configuration of $\mathrm{Cr}^{2+}$, $\mathrm{Mn}^{2+}, \mathrm{Fe}^{2+}$ and $\mathrm{Ni}^{2+}$ are $3 \mathrm{~d}^4, 3 \mathrm{~d}^5, 3 \mathrm{~d}^6$ and $3 \mathrm{~d}^8$ respectively. Which one of the following aqua complexes will exhibit the minimum paramagnetic behaviour?…

Question

The $d$ electron configuration of $\mathrm{Cr}^{2+}$, $\mathrm{Mn}^{2+}, \mathrm{Fe}^{2+}$ and $\mathrm{Ni}^{2+}$ are $3 \mathrm{~d}^4, 3 \mathrm{~d}^5, 3 \mathrm{~d}^6$ and $3 \mathrm{~d}^8$ respectively. Which one of the following aqua complexes will exhibit the minimum paramagnetic behaviour? (At. No. $\mathrm{Cr}=24, \mathrm{Mn}=25, \mathrm{Fe}=26, \mathrm{Ni}=$ 28)

Aicharya · Accepted Answer

$\begin{aligned} & \mathrm{Cr}^{++}\left(3 \mathrm{~d}^4ight)=\begin{array}{|l|l|l|l|l|} \hline \upharpoonleft & \upharpoonleft & \upharpoonleft & \upharpoonleft & \ \hline \end{array} \ & =4 	ext { unpaired } e^{-} \ & \operatorname{Mn}^{++}\left(3 \mathrm{~d}^4ight)=\begin{array}{|l|l|l|l|l|} \hline \upharpoonleft & \upharpoonleft & \upharpoonleft & \upharpoonleft & \upharpoonleft \ \hline \end{array} \ & =5 	ext { unpaired } e^{-} \ & \mathrm{Fe}^{++}\left(3 \mathrm{~d}^6ight)=\begin{array}{|l|l|l|l|l|} \hline \upharpoonleft \downharpoonright & \upharpoonleft & \upharpoonleft & \upharpoonleft & \upharpoonleft \ \hline \end{array} \ & =4 	ext { unpaired } e^{-} \ & \mathrm{Ni}^{++}\left(3 \mathrm{~d}^8ight)=\begin{array}{|l|l|l|l|l|} \hline \upharpoonleft \downharpoonright & \upharpoonleft \downharpoonright & \upharpoonleft \downharpoonright & \upharpoonleft & \upharpoonleft \ \hline \end{array} \ & =2 	ext { unpaired } e^{-} \end{aligned}$ As $\mathrm{Ni}^{++}$ has minimum no. of unpaired $e^{-}$ thus this is least paramagnetic.

The $d$ electron configuration of $\mathrm{Cr}^{2+}$, $\mathrm{Mn}^{2+}, \mathrm{Fe}^{2+}$ and…

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