Question

match the rule...
in the ground state of an atom, electrons fill lower energy orbitals first before occupying higher levels.
electron pairing only occurs after all orbitals in the same sublevel have a single electron.
two electrons in the same orbital can not exist in the same state and will have opposite spins.
drag
pauli exclusion principle
hunds rule
aufb au principle

Explanation:

The Pauli Exclusion Principle states that two electrons in the same orbital cannot exist in the same state and will have opposite spins. Hund's Rule says that electron - pairing only occurs after all orbitals in the same sublevel have a single electron. The Aufbau Principle indicates that in the ground state of an atom, electrons fill lower - energy orbitals first before occupying higher levels.

Answer:

"Two electrons in the same orbital cannot exist in the same state and will have opposite spins." - Pauli Exclusion Principle
"Electron - pairing only occurs after all orbitals in the same sublevel have a single electron." - Hund's Rule
"In the ground state of an atom, electrons fill lower - energy orbitals first before occupying higher levels." - Aufbau Principle