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Solution


Q.

Which of the following elements have half-filled f-orbitals in their ground state

(Given: atomic number Sm = 62; Eu = 63; Tb = 65; Gd = 64; Pm = 61)         [2023]

(A) Sm
(B) Eu
(C) Tb
(D) Gd
(E) Pm

Choose the correct answer from the options given below:
1 A and B only  
2 C and D only  
3 B and D only  
4 A and E only  

Ans.

(3)

Sm (Z=62)=4f6s2

Eu (Z=63)=4f76s2

Tb (Z=65)=4f96s2

Gd (Z=64)=4f75d16s2

Pm (Z=61)=4f56s2

Here Eu and Gd have half-filled configuration.