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

Explanation

Ionization enthalpies of first transition series:
(i) Ionization energy of transition element is intermediate between those of s and p block elements.
(ii) As we move from left to right in a transition metal series, the ionization enthalpy increases as expected. This is due to increase in nuclear charge corresponding to the filling of d electrons.
(iii) The increase in first ionisation enthalpy with increase in atomic number along a particular series is not regular. The added electron enters (n-1)d orbital and the inner electrons act as a shield and decrease the effect of nuclear charge on valence ns. electrons. Therefore, it leads to variation in the ionization energy values.