Bond dissociation energies in $\mathrm{kcal}\mathrm{mo}{\mathrm{l}}^{-1}$: primary C-H 101, H-Cl 103, H-Br 88. The enthalpy changes ($\Delta H$) of the hydrogen abstraction step $\mathrm{R}-\mathrm{H}+\mathrm{X}{}^{\bullet }\to \mathrm{R}{}^{\bullet }+\mathrm{H}-\mathrm{X}$ for a primary C-H bond with $\mathrm{X}=\mathrm{Cl}$ and $\mathrm{X}=\mathrm{Br}$ respectively are

1. A$+13$ and $-2$
2. B$-2$ and $+13$
3. C$-2$ and $-13$
4. D$+2$ and $-13$