JEE Main 2025 Jan 22 Shift 1, Chemistry Q5: f – Block Elements

JEE Main2025Jan 22, Shift 1Chemistry

Lanthanoid ions with $4 f^{7}$ configuration are :

(A) Eu $^{2 +}$ (B) Gd $^{3 +}$ (C) Eu $^{3 +}$ (D) Tb $^{3 +}$ (E) Sm $^{2 +}$

Choose the correct answer from the options given below :

Solution

Writing configurations after removing the appropriate number of electrons from [Xe] $4 f^{n} 6 s^{2}$ :

Eu (Z=63), Eu $^{2 +}$ : [Xe] $4 f^{7}$ $✓$

Gd (Z=64), Gd $^{3 +}$ : [Xe] $4 f^{7}$ $✓$

Eu $^{3 +}$ : [Xe] $4 f^{6}$ ; Tb $^{3 +}$ (Z=65): [Xe] $4 f^{8}$ ; Sm $^{2 +}$ (Z=62): [Xe] $4 f^{6}$ .

$∴$ Only Eu $^{2 +}$ and Gd $^{3 +}$ have $4 f^{7}$ .

Concept behind this question

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