Use ${\Delta }_i{H}_1=738$ and ${\Delta }_i{H}_2=1451$ for $\mathrm{Mg}$, and electron gain enthalpies $-141$ (first) and $+744$ (second) for $\mathrm{O}$, all in $\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$. The enthalpy change for $\mathrm{Mg}(g)+\mathrm{O}(g)\to \mathrm{Mg}{}^{2+}(g)+\mathrm{O}{}^{2-}(g)$ is

1. A$+2792\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$
2. B$+2189\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$
3. C$+1998\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$
4. D$+1586\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$