The correct increasing order of the second ionization enthalpies for Carbon (C), Nitrogen (N), Oxygen (O) and Fluorine (F) is:

Step-by-step solution

The second ionization enthalpy is the energy required to remove an electron from a unipositive cation. The electronic configurations of the unipositive ions are: C ^+ : 1s^2 2s^2 2p^1 N ^+ : 1s^2 2s^2 2p^2 O ^+ : 1s^2 2s^2 2p^3 F ^+ : 1s^2 2s^2 2p^4 Generally, ionization enthalpy increases across a period from left to right due to an increase in effective nuclear charge. Based on this general trend, the expected order would be C ^+ However, O ^+ has an exactly half-filled 2p subshell ( 2p^3 ), which imparts extra s