JEE Advanced · 2025 · 18 May 2025 · Paper 1 · d and f Block Elements

An ion is diamagnetic if it has no unpaired electrons.

${\mathrm{La}}^{3+}$: ${[}_{54}\mathrm{Xe}]4f^0$ — no unpaired electrons (diamagnetic)

${\mathrm{Ce}}^{4+}$: ${[}_{54}\mathrm{Xe}]4f^0$ — no unpaired electrons (diamagnetic)

${\mathrm{Yb}}^{2+}$: ${[}_{54}\mathrm{Xe}]4f^{14}$ — all electrons paired (diamagnetic)

${\mathrm{Lu}}^{3+}$: ${[}_{54}\mathrm{Xe}]4f^{14}$ — all electrons paired (diamagnetic)

${\mathrm{La}}^{2+}$: ${[}_{54}\mathrm{Xe}]5d^1$ — one unpaired electron (paramagnetic)

${\mathrm{Ce}}^{3+}$: ${[}_{54}\mathrm{Xe}]4f^1$ — one unpaired electron (paramagnetic)

${\mathrm{Yb}}^{3+}$: ${[}_{54}\mathrm{Xe}]4f^{13}$ — unpaired electrons (paramagnetic)

${\mathrm{Lu}}^{2+}$: ${[}_{54}\mathrm{Xe}]4f^{14}5d^1$ — one unpaired electron (paramagnetic)

Therefore, pairs (A) and (B) contain only diamagnetic ions.