ChemistryNEET 2024Lanthanoids and actinoids

The d- and f-Block Elements

The pair of lanthanoid ions which are diamagnetic is:

A. $\mathrm{Ce^{3+}}$ and $\mathrm{Eu^{2+}}$
B. $\mathrm{Gd^{3+}}$ and $\mathrm{Eu^{3+}}$
C. $\mathrm{Pm^{3+}}$ and $\mathrm{Sm^{3+}}$
D. $\mathrm{Ce^{4+}}$ and $\mathrm{Yb^{2+}}$ ✓

Solution

Diamagnetism needs no unpaired $f$ electrons. $\mathrm{Ce^{4+}}$ is $4f^0$ and $\mathrm{Yb^{2+}}$ is $4f^{14}$ — both diamagnetic. $\mathrm{Ce^{3+}}$ ( $f^1$ ), $\mathrm{Eu^{2+}}$ / $\mathrm{Gd^{3+}}$ ( $f^7$ ), $\mathrm{Eu^{3+}}$ ( $f^6$ ), $\mathrm{Pm^{3+}}$ ( $f^4$ ), $\mathrm{Sm^{3+}}$ ( $f^5$ ) are all paramagnetic.

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The d- and f-Block Elements

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