Which of the following defines high spin configurations?

High spin configurations refer to the arrangement of electrons in the d or f orbitals of transition metal complexes where the maximum number of unpaired electrons is present. This typically occurs in cases where the crystal field splitting energy is relatively small, allowing electrons to occupy higher energy orbitals rather than pairing up in lower energy orbitals.

In a high spin configuration, the electrons tend to remain unpaired to minimize the energy associated with pairing, and thus, the result is an increased number of unpaired electrons compared to what would be found in a free ion. As such, choice C accurately describes this phenomenon, highlighting that in high spin configurations, there are more unpaired electrons than in a free ion state.

The other options do not sufficiently characterize high spin systems. Pairing of electrons reduces the number of unpaired electrons, which would be seen in low spin configurations, making the idea of more paired electrons than unpaired inconsistent with the definition of high spin. Likewise, an equal number of paired and unpaired electrons does not capture the essence of a high spin setup, and stating that there are more paired electrons than in a free ion ignores the tendency of high spin complexes to favor unpaired electrons instead.