Which of the following should be correct according to Hund's rule?
Hund's rule of maximum multiplicity states that pairing of electrons in the orbitals belonging to the same subshell (p, d or f) does not take place until each orbital has got one electron i.e., it is singly occupied.
All of the electrons will have parallel spin when singly filled to attain maximum multiplicity.
There are three p, five d and seven f orbitals. Thus, pairing of electrons will start in the p, d and f orbitals with the entry of 4th, 6th and 8th electron, respectively.
Thus, electronic configuration of carbon, oxygen, nitrogen and fluorine is as follows: