Compare the ionization enthalpies of first series of the transition elements.

Explanation

(I ) Ionization energy of transition element is intermediate between those of a and p block elements .As we move from left to right in a transition icreases as expected . This is due to increase in nuclear charge corresponding to the filling of d electrons. The following figure show the trends in ionisation enthalpy of transtion elements .
(ii) The first ionisation energy of 5d series of element are much higher that those of 3d and 4d series of elements .
(iii) The added electron enters (n-1) orbital and the inner electrons act as shield and decrease the effect of nuclear charge on valence ns electrons.
(iv) therefore it leads to variation in the ionization energy values.