Among Ce 4 f 1 5 d 1 6 s 2 ,   Nd 4 f 1 6 s 2 ,   Eu 4 f 7 6 s 2 and Dy 4 f 10 6 s 2 , the elements having highest and lowest 3 rd ionisation energies, respectively are

Step-by-step solution

For 3 rd ionisation energy, the electron must be removed from + 2 oxidation state of given metals. The electronic configuration of Ce is 4 f 1 5 d 1 6 s 2 The electronic configuration of Ce 2 + is 4 f 1 5 d 1 The electronic configuration of Nd is 4 f 4 6 s 2 The electronic configuration of Nd 2 + is 4 f 4 The electronic configuration of Eu is 4 f 7 6 s 2 The electronic configuration of Eu 2 + is 4 f 7 The electronic configuration of Dy is 4 f 10 6 s 2 The electronic configuration of Dy 2 + is 4 f 10 Eu will have th