Why are the ionisation energies of 5d elements greater than 3d elements?

The ionisation energies of 6d elements are Greater than 3d elements. Give reason.

Assign reasons for the following : (b) The ionization energy of 5d elements are greater than 3d elements.

Why are I.E. of 5d - elements greater than 3d- elements ?

The ionisation energies of tranition elements are:

Why is the second ionisation energy of an element much greater than its first ionisation energy ?