NEET2026ChemistryChapterActual
The third ionisation enthalpy of Lutetium (Lu) is anomalously low. This is primarily attributed to:
Options
- Aits exceptionally small atomic radius due to lanthanoid contraction
- Bthe attainment of a highly stable completely filled 4f¹⁴ configuration
- Cthe strong shielding effect provided by the inner 5d electrons
- Dits high electronegativity compared to the early lanthanoids
Correct answer
B. the attainment of a highly stable completely filled 4f¹⁴ configuration
Step-by-step solution
The atomic number of Lutetium (Lu) is 71 . The electronic configuration of Lu is [ Xe ] 4f¹⁴ 5d¹ 6s² . During the first and second ionisations, the two 6s electrons are removed, forming Lu ²⁺ with the configuration [ Xe ] 4f¹⁴ 5d¹ . The third ionisation involves the removal of the single 5d electron. This results in the formation of Lu ³⁺ with the configuration [ Xe ] 4f¹⁴ . Since the resulting 4f¹⁴ configuration is completely filled and highly stable, the removal of the third electron requires less energy. Thus, t