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 ) Choose the correct answer from the options given below :

Step-by-step solution

f-subshell contains seven orbitals in it. Hence, if seven electrons are present in these orbitals then it said to be half-filled. Electronic configuration of all the elements are: Sm ( Z = 62 ) = 4 f 6   s 2 Eu ( Z = 63 ) = 4 f 7 6 S 2 Tb ( Z = 65 ) = 4 f 9 6 s 2 Gd ( Z = 64 ) = 4 f 7 5 d 1 6 s 2 Pm ( Z = 61 ) = 4 f 5 6 s 2 So, Eu & Gd have half-filled configuration.