The van't Hoff factor of the compound ${\mathrm{K}}_3\mathrm{Fe}(\mathrm{CN}{)}_6$ in dilute solution is 

For a diluted solution of ${\mathrm{K}}_3\left[\mathrm{Fe}\right(\mathrm{CN}{)}_6]$, the Vant Hoff factor I is 4. It splits up into 3 potassium ions and $1{\left[\mathrm{Fe}(\mathrm{CN}{)}_6\right]}^{3-}$ ion.