Q.

The electronic configurations of bivalent europium and trivalent cerium are  (atomic numbers: Xe = 54, Ce = 58, Eu = 63)

1 [Xe] 4f2 and [Xe] 4f7  
2 [Xe] 4f7 and [Xe] 4f1  
3 [Xe] 4f76s2 and [Xe] 4f26s2  
4 [Xe] 4f4 and [Xe] 4f9  

Ans.

(2)

Eu2+:[Xe] 4f7;  Ce3+:[Xe] 4f1