What elements has the highest first ionization energy out of strontium magnesium beryllium calcium?
Beryllium will have the highest. Down a group ionization energy decreases.
Calcium,barium and radium are mostly similar to strontium by properties, because these elements have the same structure of external electron orbits ( outer-shell orbitals 2s).Because of the similarity of the outer shell orbitals these elements are placed in the same group. Magnesium and beryllium have also the same structure of outer shell orbitals like strontium(2s)but they are more similar to zinc or aluminium than to strontium.