The Lanthanoids

Those element in which last electron enters in the orbital are called lanthanoid elements.
There are fourteen elements in the lanthanoid series from to .
Lanthanum is a non-lanthanoid element because the valence electron goes into -orbital not in orbital.

The general electronic configuration of lanthanides is

After the loss of both of the 65 electrons and also the solitary electrons, the lanthanoids gain stable configurations.
oxidation state is most common among lanthanides.