Question

how does the ionization energy very in group and periods ?

Answer 1

Being farther away from the positive attraction makes it easier for that electron to be pulled off. Ionization energy refers to the amount of energy needed to remove an electron from an atom. Ionization energy decreases as we go down a group. Ionization energy increases from left to right across the periodic table.

Answer 2

Ionization energy
Its an energy required to remove the electrons....

As in group Ionization energy / enthalpy
decreases
and in period it increases...