Coordination Compounds

P = [FeF$_6$]$^{3-}$ ox. no. of Fe = +3, configuration: - 3d$^5$ 4S$^D$ As F$^{-}$ is weak ligand, pairing does not take place, so it has 5 unpaired electron Q = [V(H$_2$O)$_6$]$^{2+}$ , ox. no. of V = +2, configuration: - 3d$^3$ 4S$^D$ It has 3 unpaired electrons R = [Fe(H$_2$O)$_6$]$^{2+}$ , ox. no. of Fe = +2, configuration: - 3d$^6$ 4S$^D$ As H$_2$O is weak ligand, pairing does not take place, so it has 4 unpaired electron ⇒ order of spin only magnetic moment ⇒ Q < R < P