What product is formed by mixing the solution of  ${\mathrm{K}}_4\left[\mathrm{Fe}(\mathrm{CN}{)}_6\right]$ with the solution of ${\mathrm{FeCl}}_3$ in complete absence of air?

${\mathrm{FeCl}}_3+{\mathrm{K}}_4\left[\mathrm{Fe}(\mathrm{CN}{)}_6\right]⟶{\mathrm{K}}_2\underset{(\mathrm{White} \mathrm{ppt}.)}{\mathrm{Fe}\left[\mathrm{Fe}(\mathrm{CN}{)}_6\right]}\downarrow$

If we add ferric chloride over potassium ferrocyanide, it forms a white precipitate that will become blue. because being small quantity of ferric chloride, not all potassium is displaced.