Which of the following elements have half-filled f-orbitals in their ground state? (Given: atomic number \( \mathrm{Sm} = 62 \); \( \mathrm{Eu} = 63 \); \( \mathrm{Tb} = 65 \); \( \mathrm{Gd} = 64 \), \( \mathrm{Pm} = 61 \))
A. \( \mathrm{Sm} \) B. \( \mathrm{Eu} \) C. \( \mathrm{Tb} \) D. \( \mathrm{Gd} \) E. \( \mathrm{Pm} \)
