Match List - I with List - II:

Magnetic moment $\mu =\sqrt{n(n+2)}\text{BM}$.(a) $[{\text{Fe(CN)}}_6{]}^{3-}$: ${\text{Fe}}^{3+}$ ($d^5$). ${\text{CN}}^{-}$ is strong ligand, pairs electrons $\to$ 1 unpaired electron. $\mu =1.73\text{BM}\to$ (iv).(b) $[{\text{Fe(H}}_2{\text{O)}}_6{]}^{3+}$: ${\text{Fe}}^{3+}$ ($d^5$). Water is weak ligand $\to$ 5 unpaired electrons. $\mu =5.92\text{BM}\to$ (i).(c) $[{\text{Fe(CN)}}_6{]}^{4-}$: ${\text{Fe}}^{2+}$ ($d^6$). Strong ligand pairs all electrons $\to$ 0 unpaired electrons. $\mu =0\to$ (ii).(d) $[{\text{Fe(H}}_2{\text{O)}}_6{]}^{2+}$: ${\text{Fe}}^{2+}$ ($d^6$). Weak ligand $\to$ 4 unpaired electrons. $\mu =4.90\text{BM}\to$ (iii).Sequence: (a)-(iv), (b)-(i), (c)-(ii), (d)-(iii).