Average bond energies (in kJ·mol⁻¹) for carbon–halogen bonds are: C–F 485, C–Cl 327, C–Br 285, and C–I 213. A chemist wants to modify CH₃Cl(g) so that homolytic cleavage of the carbon–halogen bond is significantly less endothermic at 298 K. Which single substitution on methane best achieves this goal?
a) CH3F(g)
b) CH3I(g)
c) CH3Br(g)
d) CH2Cl2(g)