An aqueous solution of a non-volatile solute boils at $100.17^{\circ} C$. The temperature at which this solution will freeze (in $^{\circ} C$) is
$K_{b}(H_2 O) = 0.512^{\circ} C \ kg \ mol^{-1}$,
$K_{f}(H_2 O) = 1.86^{\circ} C \ kg \ mol^{-1}$

Calculate the osmotic pressure in $atm$ at $0\,^oC$ of a $0.18\, m$ aqueous solution of $KCl$ which has a freezing point of $-0.68\,^oC$. Assume the volume of the solution is equal to the volume of pure water. $(K_f = 1.86\,^oC\, m^{-1})$

Calculate the osmotic pressure in $atm$ of an aqueous solution of urea at $37\,^oC$,which has a freezing point of $0.52\,^oC$. Assume molality and molarity are numerically equal. $(K_f = 1.86\,^oC\, m^{-1})$

$A$ non-volatile solute is dissolved in water. The $\Delta T_b$ of the resultant solution is $0.052 \ K$. What is the freezing point of the solution (in $K$)?
($K_b$ of water $= 0.52 \ K \ kg \ mol^{-1}$; $K_f$ of water $= 1.86 \ K \ kg \ mol^{-1}$,Freezing point of water $= 273 \ K$)

Calculate the solubility (in $\text{moles/litre}$) of a saturated aqueous solution of $Ag_3PO_4$ if the vapour pressure of the solution becomes $750 \ torr$ at $373 \ K$. (Assume vapour pressure of pure water at $373 \ K$ is $760 \ torr$ and density of water is $1 \ g/mL$)

Which of the following has the lowest freezing point?