JEE Main · 2023 · 13 Apr 2023 · Shift 1 · d and f Block Elements

The pair of lanthanides in which both elements have high third-ionization energy is:

(A) $Eu, Gd$
(B)Eu, Yb✓ Correct
(C) $Lu, Yb$
(D) $Dy, Gd$

Answer: (B)

Solution

The third ionization energy is high when the

M^{2 +}

ion has a stable electronic configuration.

Eu^{2 +}

has the configuration

[Xe] 4 f^{7}

(half-filled) and

Yb^{2 +}

has

[Xe] 4 f^{14}

(fully-filled). Both half-filled and fully-filled f-subshells are exceptionally stable, making the removal of a third electron (third ionization) very difficult. Hence, both Eu and Yb have high third ionization energies.

JEE Main · 2023 · 13 Apr 2023 · Shift 1 · Single correct option

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