The electronic configurations of Eu (Atomic No. 63), Gd (Atomic No. 64) and Tb (Atomic No. 65) are
[Xe]4f65d16s2,[Xe]4f75d16s2 and [Xe]4f85d16s2
[Xe]4f76s2,[Xe]4f75d16s2 and [Xe]4f96s2
[Xe]4f76s2,[Xe]4f86s2 and [Xe]4f85d16s2
[Xe]4f65d16s2,[Xe]4f75d16s2 and [Xe]4f96s2