[MnCl6]3−⇒ oxidation state of Mn is x+6(−1)‌‌=−3 x‌‌=+3‌‌(Cl‌ is weak ligand ‌) Mn‌‌=[Ar]3d54s2 Mn3+‌‌=[Ar]3d4
There are 4 unpaired electrons. [Fe(CN)6]3−⇒ oxidation state of Fe is ‌x+6(−1)=−3⇒x=+3 Fe=[Ar]3d64s2 Fe3+=[Ar]3d5 CN is strong field ligand.
1 unpaired electron in Fe3+. [Co(C2O4)3]3−⇒ oxidation state of Co is x+3(−2)‌‌=−3⇒x=+3 Co‌‌=[Ar]3d74s2 Co3+‌‌=[Ar]3d6 C2O4 is strong field ligand.