Among the following complexes, the total number of diamagnetic...

$\mathrm{Mn}^{3+} \Rightarrow[\mathrm{Ar}] 3 \mathrm{~d}^4$ $\mathrm{d}^4$ configuration in $\mathrm{t}_{2 \mathrm{~g}}$ and $\mathrm{eg}_{\mathrm{g}}$ orbitals will always have unpaired electrons irrespective of SFL and WFL. $\mathrm{Fe}^{3+} \Rightarrow[\mathrm{Ar}] 3 \mathrm{~d}^5$ $\mathrm{d}^5$ configuration will also have unpaired electron irrespective of SFL and WFL. $\mathrm{Co}^{3+} \Rightarrow[\mathrm{Ar}] 3 \mathrm{~d}^6$ $\mathrm{d}^6 \Rightarrow$ it can be both paramagnetic or diamagnetic based on field of ligands. In case of $\mathrm{F}^{-} \Rightarrow$ weak field ligand, configuration will be $\mathrm{t}_{2 \mathrm{~g}}^4 \mathrm{e}_{\mathrm{g}}^2$ hence it is paramagnetic but in case of en $\Rightarrow$ strong filed ligand, configuration will be $\mathrm{t}_{2 \mathrm{~g}}^6 \mathrm{e}_{\mathrm{g}}^0$ hence it will be diamagnetic. So, (\left[\mathrm{Mn}\left(\mathrm{NH}_3\right) 6\right]^{3+}) : Paramagnetic (\left[\mathrm{MnCl}_6\right]^{3-}) : Paramagnetic (\left[\mathrm{FeF}_6\right]^{3-}) : Paramagnetic (\left[\mathrm{CoF}_6\right]^{3-}) : Paramagnetic (\left[\mathrm{Fe}\left(\mathrm{NH}_3\right)_6\right]^{3+}) : Paramagnetic (\left[\mathrm{Co}(\mathrm{en})_3\right]^{3+}) : Diamagnetic Only 1 complex is diamagnetic.