At the freezing point of a solution containing a nonvolatile solute,which of the following are in equilibrium?

Calculate the cryoscopic constant $(K_f)$ of a solvent if the depression in freezing point of a $0.18 \ m$ solution of a non-volatile solute is $0.2 \ K$.

Identify the concentration of the solution from the following such that the values of $\Delta T_{f}$ and $K_{f}$ are the same.

The addition of $0.643 \,g$ of a compound to $50 \,mL$ of benzene (density $= 0.879 \,g \,mL^{-1}$) lowers the freezing point from $5.51^{\circ}C$ to $5.03^{\circ}C$. If the freezing point constant,$K_f$ for benzene is $5.12 \,K \,kg \,mol^{-1}$,the molar mass of the compound is approximately $..... \,g \,mol^{-1}$.

Arrange the following solutions in order of decreasing freezing points:
$(a) \ 0.075 \ M \ CuSO_4$ $(b) \ 0.060 \ M \ (NH_4)_2SO_4$
$(c) \ 0.14 \ M \ urea$ $(d) \ 0.04 \ M \ MgCl_2$

Identify $(i)$,$(ii)$ and $(iii)$ in the following diagram representing the depression in freezing point: