Question

The electronic configuration of Eu (Atomic no. 63) Gd (Atomic no. 64) and Tb (Atomic no. 65) are
a) [Xe] 4f⁶ 5d¹ 6s², [Xe] 4f⁷ 5d¹ 6s² and [Xe] 4f⁸ 5d¹ 6s²
b) [Xe] 4f⁷ , 6s², [Xe] 4f⁷ 5d¹ 6s² and [Xe] 4f⁹ 6s²
c) [Xe] 4f⁷ , 6s², [Xe] 4f⁸ 6s² and [Xe] 4f⁸ 5d¹ 6s²
d) [Xe] 4f⁶ 5d¹ 6s², [Xe] 4f⁷ 5d¹ 6s² and [Xe] 4f⁹ 6s²

Answer 1

Answer :- option (c)

Explanation :- electronic configuration of Eu(atomic number = 63) : [Xe]4f⁷ , 6s²
electronic configuration of Gd (atomic number = 64) : [Xe]4f⁸ 6s²
electronic configuration of Tb(atomic number=65) :[Xe]4f⁹ 6s²

[You should remember Afbau principle , electronic configuration is written by increasing order of energy level. higher the value of principle quantum number , hihher will be energy . If principle quantum number is same then you should check (n + l) value . For higher (n +l) value , higher will be energy level]