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- Third series has the highest first ionization energy due to poorest shielding effect of the fully filled 4fsubshell.
- This is due to lanthanoid contraction.
- Sm2+, Eu2+ and Yb2+ ions are good reducing agents as they tend to acquire common oxidation state of +3 shown by lanthanoids by the loss of one electron while Ce4+ gains one electron to attain +3. Hence, Ce4+ is an oxidising agent.
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