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

Options

A. `[Xe] 4f^(6) 5d^(1)6s^(2),[Xe] 4f^(7) 6s^(2) ` and `[Xe]4f^(8)5d^(1) 6s^(2)`
B. `[Xe] 4f^(7)6s^(2),[Xe] 4f^(7)5d^(1) 6s^(2) ` and `[Xe]4f^(9) 6s^(2)`
C. `[Xe]4f^(7)6s^(2) ,[Xe]4f^(8)6s^(2)` and `[Xe]4f^(8)5d^(1) 6s^(2)`
D. `[Xe]4f^(6) 5d^(1) 6s^(2) , [Xe]4f^(7) 65d^(1)` and `[Xe] 4f^(9) 6s^(2)`