Which aqueous solution has the minimum freezing point?

Calculate the depression in freezing point of a solution when $4 \,g$ of a nonvolatile solute with a molar mass of $126 \,g \,mol^{-1}$ is dissolved in $80 \,mL$ of water. $[$Cryoscopic constant of water $K_f = 1.86 \,K \,kg \,mol^{-1}]$ (in $\,K$)

Calculate the mass of ascorbic acid ($Vitamin \ C$,$C_6H_8O_6$) to be dissolved in $75 \ g$ of acetic acid to lower its melting point by $1.5^{\circ} C$. $\left[K_f = 3 \ K \ kg \ mol^{-1}\right]$ (in $g$)

Calculate $\Delta T_f$ of $0.15 \ m$ solution of nonvolatile solute $\left[K_f = 1.5 \ K \ kg \ mol^{-1}\right]$ (in $K$)

Give the unit of $K_f$.

The freezing point depression of a solution containing $0.6 \ g$ of urea (molar mass $= 60 \ g \ mol^{-1}$) in $100 \ mL$ of benzene (in $K$) is ($K_f$ of benzene $= 4.0 \ K \ kg \ mol^{-1}$).