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

Question

( A ) $[Xe] 4f^7 6s^2, [Xe] 4f^7 5d^1 6s^2 \; and \; [Xe] 4f^9 6s^2$
( B ) $[Xe] 4f^6 5d^1 6s^2, [Xe] 4f^7 5d^1 6s^2 \; and \; [Xe] 4f^9 6s^2$
( C ) $[Xe] 4f^6 5d^1 6s^2, [Xe] 4f^7 5d^1 6s^2 \; and \; [Xe] 4f^8 5d^1 6s^2$
( D ) $[Xe] 4f^7 6s^2, [Xe] 4f^8 6s^2 \; and \; [Xe] 4f^8 5d^1 6s^2$