# The second ionization energies of the $C,N,O$ and $F$ atoms are such that,

$(a)\;O > N > F > C \\(b)\; F > O > N > C \\ (c)\;C > O > N > F \\ (d)\;O > F > N > C$

The second ionization energy refers to the energy required to remove the electron from the corresponding mono-valent cation of the respective atom. The atoms: C, N, O and F belong to 2nd period of the periodic table.
The correct order is $O > F > N > C$
Hence d is the correct answer.
edited Oct 27, 2017