Arrange the following in the order of property indicated for each set: `F_2, Cl_2, Br_2, I_2` - increasing bond dissociation enthalpy.

Explanation

Bond dissociation enthalpy should decrease as the bond distance increases from `F_2` to `I_2` due to the corresponding increase in the size of the atom as we move from F to 1. However, the F-F bond dissociation enthalpy is smaller than that of Cl-Cl and even smaller than that of Br—Br. A reason for this anomaly is the relatively large electron-electron repulsion among the lone pairs in `F_2` molecule where they are much closer to each other than in case of `Cl_2` molecule. Thus, the bond dissociation enthalpy increases in the order :
`I_2 lt F_2 lt Br_2 lt Cl_2`