Question

The electronic configurations of Eu (Atomic No. 63), Gd (Atomic No. 64) and Tb (Atomic No. 65) are

• A. $\left[Xe\right]4f^{6}5d^{1}6s^2,\left[Xe\right]4f^{7}5d^{1}6s^{2}and\left[Xe\right]4f^{8}5d^{1}6s^2$
• B. $\left[Xe\right]4f^{7}6s^2,\left[Xe\right]4f^{7}5d^{1}6s^{2}and\left[Xe\right]4f^{9}6s^2$
• C. $\left[Xe\right]4f^{7}6s^2,\left[Xe\right]4f^{8}6s^{2}and\left[Xe\right]4f^{8}5d^{1}6s^2$
• D. $\left[Xe\right]4f^{6}5d^{1}6s^2,\left[Xe\right]4f^{7}5d^{1}6s^{2}and\left[Xe\right]4f^{9}6s^2$

Answer 1

The correct option is B $\left[Xe\right]4f^{7}6s^2,\left[Xe\right]4f^{7}5d^{1}6s^{2}and\left[Xe\right]4f^{9}6s^2$

Remember, Eu has a half filled 4f series and so does Gd. This information is enough to arrive at the correct answer.