Calculate van't Hoff-factor for 0.2 m aqueous solution of KCl which freezes at $-0.680^{\circ} \mathrm{C}$. $\left(K_f=1.86 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}\right)$

' $K$ is Henry's constant and has the unit