Acidic ferric chloride solution on treatment with excess of potassium ferrocyanide gives a Prussian blue coloured colloidal species. It is :

$\mathrm{Fe}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]_{3}$

$\mathrm{K}_{5} \mathrm{Fe}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]_{2}$

$\mathrm{HFe}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]$

$\mathrm{KFe}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]$