The orbital filling and electron configuration are based on various principles. The Aufbau principle states that electrons fill the orbital from lowest to highest energy levels. Thus, option A is correct.
The Aufbau principle is the rule that states about the filling of the electron in the various orbitals of an atom. It defines the filling of the lower atomic orbitals before the higher levels are filled.
This principle allows for determining the electronic configuration of the atom. The rule states that the electron first occupies the lowest energetically unrestricted orbits that can hold a certain number of electrons. The electron can only move to a higher level when the electron is filled in the previous subshell.
Therefore, option A. the Aufbau principle gave the filling of electrons in the lowest energy level.
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