Which element has the Lowest Second Ionization Energy?

The element with the lowest second ionization energy is typically the one that has the highest first ionization energy. This is because the second ionization energy refers to the energy required to remove a second electron from a singly charged ion.

For example, in the case of helium (He), the first ionization energy is relatively high because it's a noble gas with a full outer electron shell. However, the second ionization energy for helium is extremely high because removing a second electron would result in breaking into the stable electron configuration of helium.

So, in general, noble gases have the highest first ionization energies and thus lowest second ionization energies, because their electron configurations are very stable. Among them, helium typically has the lowest second ionization energy due to its very stable electron configuration.