Which statement best describes how electrons fill orbitals in the periodic table?

The Aufbau principle says that electrons occupy the available orbitals in order of increasing energy. Across a period, the periodic table generally shows elements being added as electrons fill these orbitals from left to right. Thus, “Electrons fill orbitals in order of their increasing energy from left to right” is the best description; the table does not fill from right to left or vertically within a group.

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