A solution of \( \mathrm{FeCl_3} \) when treated with \( \mathrm{K_4[ Fe(CN)_6 ]} \) gives a prussian blue precipitate due to the formation of:
\( \mathrm{Fe_3[ Fe(CN)_6 ]_2} \)
\( \mathrm{Fe[ Fe(CN)_6 ]} \)
\( \mathrm{K[ Fe_2(CN)_6 ]} \)
\( \mathrm{Fe_4[ Fe(CN)_6 ]_3} \)