The metal ions that have the calculated spin-only magnetic moment value of \( 4.9 \, \text{B.M.} \) are:
(A) \( \mathrm{Cr^{2+}} \)
(B) \( \mathrm{Fe^{2+}} \)
(C) \( \mathrm{Fe^{3+}} \)
(D) \( \mathrm{Co^{2+}} \)
(E) \( \mathrm{Mn^{3+}} \)
Choose the correct answer from the options given below:
