Question

The predicted order of first ionization energies from highest to lowest for gallium (Ga), germanium (Ge), selenium (Se), and arsenic (As) is
Se > As > Ge > Ga.
Ga > Ge > Se > As.
Ga > Ge > As > Se.
As > Se > Ge > Ga.

Answer 1

The order has to do with their position on the periodic table.

The ionization energy (IE) increases up any column (group) and increases to the right on any row (horizontal).