Question about particles and first ionization energy?

Question

explain in terms of atomic structure why cesium has lower first ionization energy than rubidium

Answer 1

cesium has a bigger atomic radius which makes it easier for it to lose an electron.

Answer 2

First ionization energy is the energy needed to remove one electron from an atom.

Ionization energy decreases as atomic radii increases. Radii increases going down the periodic table, so cesium has a larger radii than rubidium. Because of this, cesium has the lower first ionization energy, since it's effective nuclear charge is higher, so it's easier to remove one electron from the atom.

Therefore, cesium has lower first ionization energy than rubidium.