Which among the following lanthanoids, shows only $+3$ oxidation state?

Which among the following lanthanoids, shows only $+3$ oxidation state?
  1. Terbium
  2. Gadolinium
  3. Neodynium
  4. Cerium

Solution

Gadolinium $\rightarrow$ [Xe] $4 \mathrm{f}^{7} 5 \mathrm{~d}^{1} 6 \mathrm{~s}^{2}$ The extra stability of $\mathrm{Gd}^{3+}$ ion is due to their half-filled f-subshells.

Asked in: MHT CET 2020 (16 Oct Shift 1)

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