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

Options

A. `[Xe]4f^(7)6s^(2), [Xe]4f^(7)5d^(1)6s^(2) & [Xe] 4f^(9)6s^(2)`
B. `[Xe]4f^(7)6s^(2), [Xe]4f^(8)6s^(2)` and `[Xe]4f^(8)5d^(1)6s^(2)`
C. `[Xe]4f^(6)5d^(1)6s^(2), [Xe]4f^(7)5d^(1)6s^(2)` and `[Xe]4f^(9)6s^(2)`
D. `[Xe]4f^(5)5d^(1)6s^(2)`

Answer

A