Among the following complex ions, the one with the highest paramagnetism is: (a) \(\left[\mathrm{FeF}_{6}\right]^{2+}\) (b) \(\left[\mathrm{Cu}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\) (c) \(\left[\mathrm{Zn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}\) (d) \(\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+}\)

Imagine atoms as tiny magnets. When they get close enough to each other, the magnets' fields interact, altering the energy levels of their electrons. That's the essence of Crystal Field Theory (CFT), a model that helps us understand how metal ions in complex ions bond with molecules or ions surrounding them.

In CFT, the central idea is that ligands (the surrounding molecules or ions) create an electric field, which affects the energy of the d-orbitals of the central metal ion. These d-orbitals become split into two groups: those that will align with the ligands and thus higher in energy, and those that remain between the ligands and therefore lower in energy. This splitting is crucial because it dictates how the electrons are distributed in the d-orbitals, which in turn determines the magnetic properties of the complex ion.

Electrons orbit the nucleus of an atom in specific layers. We can think of these layers like the seats in a theater, spiraling outward. The 'electron configuration' is just a map showing which seats are taken. In transition metals, the inner 'd' seats are the ones we're most interested in because they're directly involved in bond formation.

When these metals form complex ions, some electrons might need to vacate their seats to accommodate the new charge balance. This matters because the way these electrons are arranged (paired or alone in the seats) plays a huge part in whether our 'atomic theater' is drafty or magnetically buzzing with activity.

When we're looking at the magnetic properties of a complex, we're essentially counting the number of single riders on an electron 'rollercoaster'. These are the unpaired electrons, loners not sharing their orbitals with a buddy. These solo electrons are important because each one contributes to a property called 'paramagnetism' – the more unpaired electrons, the stronger the magnetic field a complex ion can generate.

In the context of our theater analogy for electron configuration, having unpaired electrons would be like having seats occupied by just one person, with the seat next to them empty. These unoccupied seats can affect how the theater 'feels' to a passing magnet, much like single riders on the rollercoaster can make the ride more thrilling.

Imagine six friends playing a game of catch around you – that's basically what's happening in an octahedral complex. There are six ligands surrounding a central metal ion, each pair sitting opposite each other at the corners of an imaginary octagon. This arrangement is key for our discussion of paramagnetism because it influences how the d-orbitals of the central ion are split by Crystal Field Theory.

In an octahedral complex, the especially cozy pairs of electrons 'catch' lobbed energy from two different directions. This makes three of our d-orbitals boost in energy while the remaining two stay lower. The way these 'balls of energy' get distributed among these targeted zones will ultimately determine if the complex behaves like a magnetic fisherman's lure or more like a lump of clay in the magnetic sea.