Question

Why does fluorine have a higher ionization energy than iodine?

Answer 1

do you know what ionization energy is doing?

do you know how large the fluorine and iodine atoms are?

Answer 2

As you go down the period, an energy level is added (increase in atomic size). Flourine is in period 2, and Iodine is in period 5. Since the valence electrons in Iodine is farther from the nucleus (due to more energy levels), it takes less energy to take the electrons.