Explain why fluorine is more reactive than iodine, and describe the trend in boiling points as you go down Group 7.

Fluorine is more reactive than iodine because its outer shell is much closer to the nucleus, giving it a smaller atomic radius and a higher effective nuclear charge. This makes fluorine a stronger electron‑acceptor; it gains an electron more easily and attracts an incoming electron more strongly than iodine.

Boiling points increase down Group 7. The larger, more polarisable halogen atoms have stronger London dispersion forces, so iodine has a higher boiling point than bromine, which in turn is higher than chlorine and fluorine.