Answer
b. $Cl_2$ has the highest bond dissociation energy.
Work Step by Step
The bond dissociation energy decreases down the group.
The bond energy of chlorine is more than the bond energy of fluorine. This is due to the fact that the size of the fluorine atoms is very small, and the electrons on the fluorine atom repel each other due to which the bonds become weaker and the bond energy decreases.
