Which lanthanoid from following has highest ionisation ( IE ₁ ) enthalpy?

Step-by-step solution

Ionization enthalpy increases across the lanthanoid series due to the increasing nuclear charge combined with the poor shielding effect of 4f electrons. Neodymium (Nd, Z=60): [Xe] 4f ^4 6s ^2 , IE1 ≈ 533.1 kJ/mol Dysprosium (Dy, Z=66): [Xe] 4f ¹⁰ 6s ^2 , IE1 ≈ 573.0 kJ/mol Thulium (Tm, Z=69): [Xe] 4f ¹² 6s ^2 , IE1 ≈ 596.7 kJ/mol Ytterbium (Yb, Z=70): [Xe] 4f ¹⁴ 6s ^2 , IE1 ≈ 603.4 kJ/mol The magnitude of IE1 increases with atomic number as the effective nuclear charge grows. Ytterbium shows the highest ionization