Which lanthanoid commonly exhibits both +2 and +3 oxidation states due to extra stability of half-filled f-orbitals?
Europium (Eu) shows +2 oxidation state due to the stability of half-filled 4f 7 configuration, along with the common +3 state.
Ref: NCERT Class 12 Chemistry > Chapter 4: d and f Block Elements > Topic: Oxidation States and Colour and Magnetic Properties of d-Block
