Why are the second and third ionisation energies of group 13 elements much higher as compared to their first ionisation energies?

Explanation

(a) After the removal of first electron, the effective nuclear charge increases.
(b) As a result, the remaining electrons experience a greater nuclear pull and thus it becomes difficult to remove second and third electrons
(c ) Moreover, second and third electrons is to be removed from s-orbitals which are less penetrating and are more tightly held by the nucleus.
(d) Therefore, a large amount of energy is required to remove second or third electron from an atom of group 13 elements.