\( \mathrm{Fe^{3+}} \) cation gives a Prussian blue precipitate on addition of potassium ferrocyanide solution due to the formation of:
\( \left[\mathrm{Fe(H_2O)_6}\right]_2 \left[\mathrm{Fe(CN)_6}\right] \)
\( \mathrm{Fe_2}\left[\mathrm{Fe(CN)_6}\right]_2 \)
\( \mathrm{Fe_3}\left[\mathrm{Fe(OH)_2(CN)_4}\right]_2 \)
\( \mathrm{Fe_4}\left[\mathrm{Fe(CN)_6}\right]_3 \)
