F2 is gas but I2 is solid, because

Larger London forces are present in I2 when compared to F2 .The molecules of each substance attract each other through dispersion (London) intermolecular forces.Whether a substance is a solid, liquid, or gas depends on the balance between the kinetic energies of the molecules and their intermolecular attractions. Molecules at the same temp have the same average kinetic energy In fluorine, the electrons are tightly held to the nuclei. The electrons have little chance to wander to one side of the molecule, so the London dispersion forces are relatively weakIn iodine, the electrons are so far from the nuclei that the electron clouds can easily distort. The London dispersion forces are strong.