what is re-organisation energy in transition elements..and how is this related to ionisation enthalpies of these elements..??

Dear Student, Reorganization energy is the energy which is used for the rearrangement of the electrons. 

Understand it by taking an example of Cr.

Electronic configuration of the Cr = 3d⁴4s²

Which after the rearrangement = 3d⁵4s¹ 

rearrangement is done because of getting the stable half filled electronic configuration.

So the energy used for the transfer of one electron from the s orbital to the d orbital  to get new arrangement is the reorganization energy.

Whereas ionization energy is simply the energy used for the removal of the outermost loosely held electron from the isolated gaseous atom.