The correct order of bond dissociation enthalpy of halogens is :

<p>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.</p> <p>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.</p> <p>Thus, the order of $\Delta$_dissH$^\circ$ (in kJ mol^$-$1) is</p> <p>$$\mathop {Cl - Cl}\limits_{(242.6)} > \mathop {Br - Br}\limits_{(192.3)} > \mathop {F - F}\limits_{(158.8)\,Electrostatic\,repulsion} > \mathop {I - I}\limits_{(151.1)\,Steric\,repulsion} $$</p>