Find correct order of ionization enthalpy among F, Cl, Cl⁻ and F⁻.

Solution:

Negative ions have lower ionization enthalpy than neutral atoms because extra electron is easier to remove.

Smaller size increases ionization enthalpy.

Therefore:

F > Cl > F⁻ > Cl⁻

Answer:

F > Cl > F⁻ > Cl⁻