Arrange the following species in order of decreasing first ionization energy: rn mg he ar

To arrange the following species in order of decreasing first ionization energy you have to remember that it depends on difficulty of removing a valence. And according to this statement, it should be like this  Ra , Kr and Ne, then we put Mg as this atom has the lowest ionization energy value. Hope everything is clear! Regards!

Wikipedia aswell can be used to solve the following questions