Which of the following properties increases from fluorine to iodine...

As we move down the group from fluorine to iodine, the number of electron shells increases. Consequently, the atomic and ionic radii increase.

Electronegativity decreases down the group due to the increase in atomic size.

Volatility decreases down the group because the magnitude of van der Waals forces of attraction increases with an increase in molecular size and mass (fluorine is a gas, whereas iodine is a solid).

Oxidizing power decreases down the group because the standard reduction potential decreases from fluorine to iodine.

Thus, only the ionic radius increases from fluorine to iodine.

Answer: Ionic radius