Answer:
Fe^3+
Explanation:
The electron configuration for Fe^3+ is; 1s2 2s2 2p6 3s2 3p6 3d5
The electron configuration for Ni^2+ is; 1s2 2s2 2p6 3s2 3p6 3d8
Now it is pertinent to recall that the 3d sublevel has a maximum occupancy of ten electrons. These ten electrons occupy a set of five degenerate orbitals. Having said that, it is clear that Ni^2+ ion will have two unpaired electrons while Fe^3+ will have five unpaired electrons.
Let us also not forget that paramagnetism has to do with the presence of unpaired electrons. That means that maximum paramagnetism refers to the presence of maximum number of unpaired electrons.
Since Fe^3+ has the greatest number of unpaired electrons among the duo, Fe^3+ will exhibit a maximum paramagnetic behavior.
