The First Ionization Energy of Gallium Is Greater Than That

Multiple Choice

The first ionization energy of gallium is greater than that of aluminum and the first ionization energy of thallium is greater than that of indium.A possible explanation for this is

A) This is the normal trend in ionization energy.
B) Both Ga and Tl prefer to lose three electrons rather than one.
C) Both Ga and Tl follow transition elements which are excellent shielders of nuclear charge.
D) Ga follows a series of transition elements and Tl follows both a series of transition elements and inner transition elements which are poor shielders of nuclear charge.