FIRST ionization ENERGY is the energy required to remove one mole of the most loosely held ELECTRONS from one mole of gaseous atoms.Ti → |Ar|3d2 4s2Mn → |Ar|3d5 4s2Ni → |Ar|3d8 4s2Zn → |Ar|3d10 4s2The PROCESS of removing electrons from shells with more electrons is easier than removing electrons from the shell with less electrons.Thus, the correct order of the first ionization ENTHALPIES is:Ti < Mn < Ni < Zn