The correct option is C O>F>N>C
The second ionisation energy means the energy required to remove the electron from the corresponding monovalent cation of the respective atom. For IE2, electronic configuration of C+,N+,O+ and F+-ions which are as follows.
∵ O+ is half-filed configuration, obviously it is most stable and greater ionisation energy than F+ as well as N+.
The ionisation energy of an element depends upon its size as. Hence, correct order will be, O>F>N>C.