Identify the elements of alkali metals and alkaline earth metals respectively having highest 1st ionization enthalpy.

Step-by-step solution

Ionization enthalpy decreases down a group in the periodic table due to an increase in atomic size and shielding effect. Among alkali metals (Group 1), Lithium ( Li ) is at the top of the group and has the smallest atomic size, hence it has the highest first ionization enthalpy. Among alkaline earth metals (Group 2), Beryllium ( Be ) is at the top of the group and has the smallest atomic size, hence it has the highest first ionization enthalpy. Therefore, the elements with the highest first ionization enthalpy are