The ionisation enthalpies of $\mathrm{Na}$ are ${\Delta }_i{H}_1=496$ and ${\Delta }_i{H}_2=4562$ $\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$; those of $\mathrm{Mg}$ are 738 and $1451\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$; ${\Delta }_i{H}_3(\mathrm{Mg})=7733$. Which statements are correct?

1. AFor $\mathrm{Mg}$, ${\Delta }_i{H}_2>{\Delta }_i{H}_1$
2. BThe first ionisation enthalpy of $\mathrm{Na}$ is lower than that of $\mathrm{Mg}$
3. CThe second ionisation enthalpy of $\mathrm{Na}$ is greater than that of $\mathrm{Mg}$
4. DFor $\mathrm{Mg}$, ${\Delta }_i{H}_3<{\Delta }_i{H}_2$