Question

in a many-electron atom, can we predict unambiguously whether the 4s orbital is lower or higher in energy than the 3d orbitals?

Answer 1

Answer: No

Step-by-step explanation:

because the relative energies of these orbitals depend on the specific electronic configuration of the atom and the effective nuclear charge experienced by the valence electrons. In some cases, the 4s orbital may be lower in energy and fill before the 3d orbitals, while in other cases the 3d orbitals may be lower in energy and fill before the 4s orbital.