Name a member of the lanthanoid series: (I) which exhibits +4 oxidation state; (II) which exhibits +2 oxidation state.
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Solution and Explanation
Answer:
(I) +4 oxidation state: Cerium (Ce). On losing four electrons Ce4+ reaches the stable empty 4f0 configuration, so Ce shows +4. (Praseodymium, Pr, and terbium, Tb, also show +4.)
(II) +2 oxidation state: Europium (Eu). Eu2+ has the stable half-filled 4f7 configuration, so Eu shows +2. (Ytterbium, Yb, with 4f14, and samarium, Sm, also show +2.)
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