(a) [Fe(CN)6]3- Oxidation state of Fe=+3
It has one unpaired electron and is paramagnetic.
(b) It has two unpaired electrons and is paramagnetic
(c) It has no unpaired electron and is diamagnetic
(d) $\therefore$ It is paramagnetic as it has five unpaired electrons.
$5 {Fe}^{2+}+{MnO}_{4}^{-}+8 {H}^{+} \rightarrow {Mn}^{2+}+4 {H}_{2} {O}+5 {Fe}^{3+}$
$(A)\,\,\,\,[Ni(H_2O)_5NH_3]^{2+},$
$(B)\,\,\,\,[Ni(H_2O)_4(NH_3)_2]^{2+}$
$(C)\,\,\,\,[Ni(H_2O)_3(NH_3)_3]^{2+}$