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In the context of lanthanoids (elements La through Lu), which of the following statements are correct? (Select all that apply.)

1. Because of similar properties, the separation of lanthanoids is not easy.
2. The availability of 4f electrons results in the formation of compounds in the +4 state for all members of the series.
3. There is a gradual decrease in the radii of the members with increasing atomic number in the series.
4. All members of the series exhibit the +3 oxidation state.

Correct answer: Because of similar properties, the separation of lanthanoids is not easy.

Solution

A: TRUE — lanthanoids have very similar chemical properties due to similar outer electronic configurations, making their separation by conventional methods difficult (ion-exchange chromatography is needed). B: FALSE — not all lanthanoids form +4 compounds; only Ce, Pr, and Tb commonly do. C: TRUE — lanthanoid contraction: successive addition to 4f subshell provides poor shielding, leading to gradual decrease in ionic/atomic radius across the series. D: TRUE — all lanthanoids exhibit the +3 oxidation state as their characteristic and common state.

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