Step1 In the second period Li has the highest second ionization energy as the 2nd electron is being removed from a stable 1s2 configuration. Step2 Be has lowest 2nd ionization energy ; as removal of 2 electrons leads to a stable 1s2 configuration. Step3 O has highest 2nd ionization energy as the 2nd electron is being removed from a half filled 2p subshell. N has lowest as removal is from a partly filled 2p shell. Also between N and F ; following the general periodic trend N has second ionization energy less than F. Solution Step1 In the second period Li has the highest second ionization energy as the 2nd electron is being removed from a stable 1s2 configuration. Step2 Be has lowest 2nd ionization energy ; as removal of 2 electrons leads to a stable 1s2 configuration. Step3 O has highest 2nd ionization energy as the 2nd electron is being removed from a half filled 2p subshell. N has lowest as removal is from a partly filled 2p shell. Also between N and F ; following the general periodic trend N has second ionization energy less than F..