= Solution
Ignoring ligand perturbations initially, end-on $d_{z^2}$ overlap gives the largest <sigma bond> splitting, side-on $d_{xz},d_{yz}$ overlap gives the two <pi bonds>, and the two four-lobed overlaps give weaker <delta bonds>. A useful qualitative ordering is
$$
\boxed{a_{1g}(\sigma)<e_u(\pi)<\{b_{2g},b_{1g}\}(\delta)
<\{b_{1u},b_{2u}\}(\delta^*)<e_g(\pi^*)<a_{2u}(\sigma^*).}
$$
The original diagram shows the ten orbitals, including both members of each $e$ level.
\Image[/past-exam-of-the-chemistry-a-course-of-the-university-of-cambridge/2024/paper-1-metal-orbitals.png]
{title=Original qualitative ordering of ten metal 4d symmetry orbitals before ligand perturbation}
For the strictly isolated collinear metal pair, cylindrical symmetry makes $d_{xy}$ and $d_{x^2-y^2}$ related by rotation, so the two delta bonding levels are degenerate, as are their antibonding partners. The displayed <D4h molecular point group> labels anticipate the ligand environment, which can split those different irreps. Symmetry supplies labels and degeneracies; the relative separation of unrelated levels is a qualitative overlap model, not a numerical prediction.
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