Question

The $+3$ ion of which one of the following has half-filled $4f$ subshell?

• A. $La$
• B. $Lu$
• C. $Gd$
• D. $Ac$

Answer 1

The correct option is C $Gd$

Lanthanum- $\left[Xe\right]5d^{1}6s^2$

$L{a}^{3+}-\left[Xe\right]$

Luthenium- $\left[Xe\right]4f^{14}5d^{1}6s^2$

$L{u}^{3+}-\left[Xe\right]4f^{14}$

Gadolinium- $\left[Xe\right]4f^{7}5d^{1}6s^2$

$G{d}^{3+}-\left[Xe\right]4f^7$

Actinium- $\left[Rn\right]6d^{1}7s^2$

$A{c}^{3+}-\left[Rn\right]$