which element has the highest first ionization energy among; Ca, Se,O?

is it O? because it's above the other two elements?
Please explain

Question

which element has the highest first ionization energy among; Ca, Se,O? 

is it O? because it's above the other two elements? 
Please explain

wolfe8 · Answer

I would say so since higher in the periodic table means smaller shells. Smaller shells mean stronger attraction between electrons and nucleus. Might wanna make sure.

gudden · Answer

Ca cannot have high first ionization energy... cuz ... it is a metal... with just 2 valence electrons...

and since  O and Se.. lie in the same group and as we move down a group the size of the atom increases..... increasing the outermost shell's distance from the nucleus...

and therefore... u are correct... that Ozygen has a higher first ionization energy than Se...