Explanation

(a)
Halogen $F_{2}$ $Cl_{2}$ $Br_{2}$ $I_{2}$
Bond dissociation 158.8 242.6 192.8 151.1
Energy (kJ $mol^{1}$)
The bond dissociation energy of $F_{2}$ is less than $Cl_{2}$ due to inter electronic repulsions present in small atom of fluorine.
The order of bond energy is $Cl_{2}$ >$F_{2}$ > $Br_{2}$ > $I_{2}$ and
$Cl_{2}$ has maximum bond energy.