d-f Block Elements

Which of the 3d series of the transition metals exhibits the largest number of oxidation states and why?

Why do transition metals exhibit higher enthalpies of atomisation ?

The chemistry of the actionoid elements is not so smooth as that of the lanthanoids. Justify this statement by giving some examples from the oxidation state of these elements.

Why is Cr²⁺ reducing and Mn³⁺ oxidising when both have d⁴ configuration?

Why is the Eº values for Mn³⁺/Mn²⁺ couple much more positive than for Cr³⁺/Cr²⁺ or Fe³⁺/Fe²⁺ ?

Compare the chemistry of actinoids with that of lanthanoids with special reference to 

(i) Electronic configuration

(ii) oxidation state

(iii) atomic and ionic sizes 

In what way is the electronic configuration of transition elements different from that of the non-transition elements?

Explain briefly how +2 state becomes more and more stable in the first half of the first row transition elements with increasing atomic number.