Here's why:

* Intermolecular forces: The strength of intermolecular forces between molecules determines the boiling point. Iodine has stronger London dispersion forces (a type of Van der Waals force) than chlorine due to its larger size and greater number of electrons.

* Size and Polarizability: Iodine atoms are much larger than chlorine atoms. This means they are more polarizable, meaning their electron clouds can be distorted more easily. Greater polarizability leads to stronger London dispersion forces.

Boiling Points:

* Chlorine (Cl2): -34.04 °C

* Iodine (I2): 184.3 °C

Therefore, iodine's stronger intermolecular forces require more energy to overcome, resulting in a higher boiling point.