Answer
Chlorine has a higher effective nuclear charge, and therefore should be more oxidizing than iodine.
Explanation:
The nuclear charge of chlorine is less shielded by intervening electrons. Thus chlorine gas should be a better oxidant.
If we turn to reduction potentials, which we should do as scientists because scientists must utilize quantitative data, we find:
12Cl2e−→Cl−E∘=1.36
12I2+e−I−E0=0.54
How is this consistent with the given proposition?