Number of complexes with even number of electrons in \( t_{2g} \) orbitals is:
\( [\mathrm{Fe}(\mathrm{H}_2\mathrm{O})_6]^{2+} \), \( [\mathrm{Co}(\mathrm{H}_2\mathrm{O})_6]^{2+} \), \( [\mathrm{Co}(\mathrm{H}_2\mathrm{O})_6]^{3+} \), \( [\mathrm{Cu}(\mathrm{H}_2\mathrm{O})_6]^{2+} \), \( [\mathrm{Cr}(\mathrm{H}_2\mathrm{O})_6]^{2+} \)