Option (ii) [Fe(H2O)6]2+ has the highest magnetic moment. To determine this, we calculate the number of unpaired electrons in each complex. [Cr(H2O)6]3+ contains Cr3+ with d3 configuration, which has 3 unpaired electrons as stated in the context that 'for metal ions with upto three electrons in the d orbitals... Cr3+ (d3)... The magnetic behaviour of these free ions and their coordination entities is similar.' [Fe(H2O)6]2+ contains Fe2+ with d6 configuration. Since H2O is a weak field ligand (similar to F- mentioned in context), it forms an outer orbital or high spin complex. The context shows that '[CoF6]3- is paramagnetic with four unpaired electrons' for d6 Co3+ with weak field ligand, so by analogy, Fe2+ (d6) with H2O also has 4 unpaired electrons. [Zn(H2O)6]2+ contains Zn2+ with d10 configuration (fully filled), having zero unpaired electrons and is diamagnetic. Since magnetic moment depends on the number of unpaired electrons, [Fe(H2O)6]2+ with 4 unpaired electrons has the highest magnetic moment value.