Name the members of the lanthanoid series which exhibit (+4) oxidation states and those which exhibit (+2) oxidation states. Try to correlate this type of behaviour with the electronic configurations of these elements.

Explanation

Elements Ce(Z=58), Pr(Z=59), Tb(Z=65) and Dy(Z=66) show (+4) oxidation state. While elements Nd(Z=60), Pm(Z=61), Sm(Z=62), Eu(Z=63), Tm (Z=69) and Yb(Z=70) show (+2) oxidation states.
(+2) and (+4) oxidation states occur when the configuration `f^(0), f^(7) and f^(14)` are attained by the elements.
(i) `Ce^(4+) (f^(0)) rArr (+4)` Oxidation state.
(ii) `Eu^(2+) (f^(7) rArr (+2)` Oxidation state.
(iii) `Yb^(2+) (f^(14)) rArr (+2)` Oxidation state.