Variability in the oxidation states of lanthanides is limited. Why? 

Explanation

The common oxidation state of lanthanides is + 3. Existence of +2 and +4 states is due to the fact that empty , half - filled or completely f-subshells provide lower energy and ions get stabilised. `Ce^(4+)` has `f^0, Tb^(4+)` ha `f^7,Eu^(2+) and Yb^(2+)` has `f^14` stable configurationns.