Duduli

Answer:- According to this principle“electrons are filled in various molecular orbitals in the increasing order of their energies”(,i.e molecular orbital with less energy is filled first.

Answer:- According to Pauli's exclusion principle, an orbital can have a maximum of two electrons and these two electrons must be of opposite spin.

Answer:- According to this rule,“no electron pairing takes place in the orbitals of p,d and f-subshells  until each orbital is singly filled with electrons having parallel spins.”