Which complex among the following is most paramagnetic?

Which complex among the following is most paramagnetic?
  1. $\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{2+}$
  2. $\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+}$
  3. $\left[\mathrm{Co}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}$
  4. $\left[\mathrm{Co}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{3+}$

Solution

$\begin{array}{|l|c|c|c|c|}\hline \text{Complex} & \begin{array}{c} \text{Metal} \\ \text{oxidation} \\ \text{state} \end{array} & \text{EC} & \begin{array}{c} \text{Nature} \\ \text{of ligand} \end{array} & \begin{array}{c} \text{No. of} \\ \text{unpaired electron} \end{array} \\ \hline\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{2+} & \mathrm{Co}^{2+} & 3 \mathrm{~d}^7 & \text{Strong} & 1 \\ \hline\left[\mathrm{Co}\left(\mathrm{NH}_3\right)_6\right]^{3+} & \mathrm{Co}^{3+} & 3 \mathrm{~d}^6 & \text{Strong} & 0 \\ \hline\left[\mathrm{Co}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{3+} & \mathrm{Co}^{2+} & 3 \mathrm{~d}^7 & \text{Weak} & 3 \\ \hline\left[\mathrm{Co}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{3+} & \mathrm{co}^{3+} & 3 \mathrm{~d}^6 & \text{Strong} & 0 \\ \hline\end{array}$
So, 'c' is the correct option. but offical answer given is d.

Asked in: AP EAMCET 2024 (22 May Shift 2)

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