Consider the transition metal ions $Mn^{3+}$, $Cr^{3+}$, $Fe^{3+}$, and $Co^{3+}$. All form low spin octahedral complexes. The correct decreasing order of unpaired electrons in their respective $d$-orbitals of the complexes is:

• A
  $Cr^{3+} > Mn^{3+} > Fe^{3+} > Co^{3+}$
• B
  $Mn^{3+} > Fe^{3+} > Co^{3+} > Cr^{3+}$
• C
  $Fe^{3+} > Mn^{3+} > Cr^{3+} > Co^{3+}$
• D
  $Co^{3+} > Fe^{3+} > Mn^{3+} > Cr^{3+}$