Among halogens (F₂, Cl₂, Br₂ and I₂), bond dissociation enthalpy ($$\Delta$$_dissH$$^\circ$$) of I₂, is minimum because of larger size of I-atom there is a steric repulsion between bonded I-atoms, which makes I-I bond weakest.

Whereas, smaller size and highest electronegativity of F-atom cause highest electron density on F-atom of F₂ molecule. As a result, F-F bond becomes weaker due to electrostatic repulsion between bonded F-atoms.

Thus, the order of $$\Delta$$_dissH$$^\circ$$ (in kJ mol^$$-$$1) is

$$\mathop {Cl - Cl}\limits_{(242.6)} > \mathop {Br - Br}\limits_{(192.3)} > \mathop {F - F}\limits_{(158.8)\,Electrostatic\,repulsion} > \mathop {I - I}\limits_{(151.1)\,Steric\,repulsion} $$