Transition metal complex with highest value of crystal field splitting \( (\Delta_0) \) will be:
\( [\mathrm{Cr(H_2O)_6}]^{3+} \)
\( [\mathrm{Mo(H_2O)_6}]^{3+} \)
\( [\mathrm{Fe(H_2O)_6}]^{3+} \)
\( [\mathrm{Os(H_2O)_6}]^{3+} \)