Answer:
Hund's rule
Pauli exclusion theory
Aufbau principle
Explanation:
Hund's rule states that, in the filling of degenerate orbitals, electrons occur singly first before pairing takes place.
Pauli exclusion theory states that no two electrons in the same atom can have the same value for all four quantum numbers.
Aufbau principle states that lower energy orbitals are first filled before the higher energy orbitals.
