Answer: Fluorine has the highest ionization enthalpy.
Explanation: This is because the ionization energy decreases from top to bottom and increases from left to right. Also, ionization enthalpy is the amount of energy required by an isolated gaseous atom to lose an electron in its ground state.
Since fluorine needs just one atom to attain noble gas configuration so it will not want to lose any electron and hence a high amount of energy will be required to remove an electron from it.
