Answer:
RULES FOR FILLING MOLECULAR ORBITALS
Aufbau's principle
molecular orbitals with electrons are filled in the increasing order of their energies.this principle is called Aufbau's principle
Pauli's exclusion principle
A molecular orbital like atomic orbital can accommodate only two electrons with opposite spins as required bu Pauli's exclusion principle
Hund's rule of maximum multiplicity
in molecular orbital no electron pairing takes place until all the available orbitals of identical energy are singly occupied.this is Hund's rule of maximum multiplicity.