The correct option is A O>F>N>C
The electronic configurations of ions after first ionization are:
As we go across a period, Zeff increases because valence electrons do not screen the nuclear charge effectively. Hence, the IP's increase across a period. But, oxygen has more second ionisation potential than fluorine. This is because after the first ionisation, oxygen acquires stable half filled configuration. Thus, for the second ionisation, electron has to be removed from 2p3 sub-shell. While in the case of fluorine, it is getting removed from 2p4 sub-shell.