Account for the following statements:

a. The difference in the ionization energies between any two successive d-block elements is less than the difference in case of successive s-block elements.

The reason to support the statement:

In case of d-block elements, the electron does not get added in the outermost shell but in the penultimate shell. So,, as the number of electrons increases in the penultimate shell, the screening effect provided by the penultimate shell to the outermost s-orbital also increases. Thus, the outermost s-electrons are shielded from the nuclear pull.

In the case of s-block elements there is no such increases in screening, and the second successive element in the period has a fully filled orbital, which is  more stable than half-filled. Thus more energy is required to remove that electron.

Thus, the difference in the ionization energies between any two successive d-block elements is less than the difference in case of successive s-block elements.