b
\(\ln \mathrm{K}_{4}\left|\mathrm{F} e(\mathrm{CN})_{6}\right|\)

\(\mathrm{Fe}(26)=3 \mathrm{d}^{6} 4 s^{2}\)

\(\mathrm{Fe}^{+2}=3 \mathrm{d}^{6}\)

In presence of \(\mathrm{SFL}\;\;\; 3 \mathrm{d}^{6} \rightarrow \mathrm{t}_{2 \mathrm{g}}^{6} \mathrm{e}_{\mathrm{g}}^{\circ}\)