Helium has the highest first ionization energy and francium has the lowest first ionization energy.
One can recognize a periodic trend on the periodic table by observing properties of different elements from the left side to the right side of the periodic table.
Barium(Ba)
Excepting groups 5-12 of the periodic table.the atomic radius increase down in the group.
magnesium (Mg)
question: which of the following elements is the smallest?
answer: chlorine (CI)
For example this is a salt.