The trend in ionization energy that occurs across a period on periodic table is that
Ionization energy of elements within a period generally increases from left to the right.
explanation
Ionization energy is energy required to remove an electron from gaseous atom or ion.
The ionization energy increase across the period because, as you move across the period (from the left to the right) the atomic radius decrease.
This make outer electrons to be closer to the nucleus and more attracted to the center.Therefore it is hard to remove electron as you move across the period.
