Question

what rule/principle states that electrons fill orbitals from lowest energy to highest energy?
aufbau principle
hunds rule
pauli exclusion principle

Explanation:

The Aufbau principle dictates that electrons occupy orbitals starting from the lowest - energy ones and moving to higher - energy ones. Hund's rule is about maximizing the number of unpaired electrons in degenerate orbitals. The Pauli exclusion principle states that no two electrons in an atom can have the same set of four quantum numbers.

Answer:

Aufbau principle