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JEE Main 2024 · Chemistry · d- and f-Block Elements and Metallurgy · easy

Among the trivalent lanthanide ions Gd^3+, Eu^3+, Dy^3+ and Lu^3+, the ion having the highest spin-only magnetic moment is

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Among the trivalent lanthanide ions Gd3+\mathrm{Gd^{3+}}, Eu3+\mathrm{Eu^{3+}}, Dy3+\mathrm{Dy^{3+}} and Lu3+\mathrm{Lu^{3+}}, the ion having the highest spin-only magnetic moment is
  1. A. Gd3+\mathrm{Gd^{3+}}
  2. B. Eu3+\mathrm{Eu^{3+}}
  3. C. Dy3+\mathrm{Dy^{3+}}
  4. D. Lu3+\mathrm{Lu^{3+}}
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Answer: (A) Gd3+\mathrm{Gd^{3+}}

Electronic configurations: Gd3+=4f7\mathrm{Gd^{3+}}=4f^7 (7 unpaired electrons), Eu3+=4f6\mathrm{Eu^{3+}}=4f^6 (6), Dy3+=4f9\mathrm{Dy^{3+}}=4f^9 (5) and Lu3+=4f14\mathrm{Lu^{3+}}=4f^{14} (0). Spin-only μ=n(n+2)\mu=\sqrt{n(n+2)} BM is largest for n=7n=7: μ=63=7.94\mu=\sqrt{63}=7.94 BM.
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