What is primarily affected by the treatment of electron-electron repulsions as negligible?

When electron-electron repulsions are treated as negligible, it primarily affects the energies of microstates. In quantum mechanics and statistical thermodynamics, microstates refer to the specific arrangements of electrons in various orbitals that correspond to a particular configuration of a system. Each microstate has an associated energy, and the overall energy depends on how these electrons interact with each other.

In a system where electron-electron repulsions are neglected, we may derive a simplified model that focuses on single-electron energies without considering these interactions, resulting in a different quantification of those microstate energies. This can significantly alter the predicted distribution of electrons among the available energy levels and molecular orbitals because the energies are determined without accounting for the stabilizing or destabilizing effects of repulsion between electrons.

In contrast, the other options pertain to different aspects of atomic or molecular structure. The orbital shapes are determined primarily by quantum numbers and the underlying quantum mechanical nature of the orbitals, while molecular geometry is largely defined by the spatial arrangement of bonded pairs and lone pairs of electrons. The electron configuration can represent how electrons fill these orbitals according to the Aufbau principle and does not change simply due to the treatment of electron repulsion.

Thus, the correct choice emphasizes how