Give a brief explanation of the ionisation enthalpy of alkaline earth metals (Group-$2$) elements.

(N/A) The alkaline earth metals have low ionisation enthalpies due to the fairly large size of their atoms.
As the atomic size increases down the group,the ionisation enthalpy decreases.
The first ionisation enthalpies of the alkaline earth metals are higher than those of the corresponding Group-$1$ metals because of their smaller atomic size compared to the alkali metals.
It is interesting to note that the second ionisation enthalpies of the alkaline earth metals are smaller than those of the corresponding alkali metals.