Why 5d transition series has highest ie1than 3d and 4d

1st ionisation energies of 5d elements are higher than those of 3d or 4d elements this is due to the greater effective nuclear charge acting on outer valence electrons because of w...

Simply lanthanide contraction

5d elements have almost the same radius as that of 4d due to lanthanide contraction but they experienced greater effective nuclear charge because of the weak shielding of the nucle...

See 5d have more shielding effect than 4f. So 5d eletron penetrates more towards the nucleus