The complex with highest magnitude of crystal field splitting energy ∆ 0 is

Crystal field stabilisation energy of the complex can be calculated as follows,

CFSE = $\mathrm{number} \mathrm{of} {\mathrm{t}}_{2\mathrm{g}} \mathrm{electrons}\times \left(-0.4\right)+\mathrm{number} \mathrm{of} {\mathrm{e}}_{\mathrm{g}} \mathrm{electrons}\times \left(0.6\right)$

Complex                    CFSE

${\left[\mathrm{Ti}{\left({\mathrm{OH}}_2\right)}_6\right]}^{3+}\left({{\mathrm{t}}_{2\mathrm{g}}}^1{{\mathrm{e}}_{\mathrm{g}}}^0\right)$        $–0.4 {∆}_0$

${\left[\mathrm{Cr}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{3+}\left({{\mathrm{t}}_{2\mathrm{g}}}^3{{\mathrm{e}}_{\mathrm{g}}}^0\right)$        $–1.2 {∆}_0$

${\left[\mathrm{Mn}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{3+}\left({{\mathrm{t}}_{2\mathrm{g}}}^3{{\mathrm{e}}_{\mathrm{g}}}^1\right)$        $–0.6 {∆}_0$

${\left[\mathrm{Fe}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{3+}\left({{\mathrm{t}}_{2\mathrm{g}}}^3{{\mathrm{e}}_{\mathrm{g}}}^2\right)$         $0$