JEE Main · 2022 · 26 Jun 2022 · Shift 2 · d and f Block Elements

Cerium (Ce) can easily deviate from the +3 oxidation state to +4.

Electronic configuration:

• Ce: [Xe] $4f^{1}5d^{1}6s^2$
• $\mathrm{Ce}{}^{3+}$: [Xe] $4f^1$
• $\mathrm{Ce}{}^{4+}$: [Xe] $4f^0$ (noble gas configuration)

The +4 oxidation state of cerium is particularly stable because it achieves a noble gas configuration with an empty 4f subshell. This makes Ce the lanthanoid most likely to deviate from the +3 oxidation state.

The other lanthanoids listed do not achieve such stable configurations in the +4 state.