Which of the following aqueous solutions exhibits the lowest freezing point depression, assuming complete dissociation?

The freezing point of a solution containing $1.25 \ g$ of a non-electrolyte solute in $20 \ g$ of water is $271.9 \ K$. What is the molar mass of the solute? (Given: $K_f$ for water = $1.86 \ K \ kg \ mol^{-1}$,Freezing point of pure water = $273 \ K$)

$x$ moles of $CO(NH_2)_2$ are present in $1200 \ g$ of water. If the freezing point of the solution is $-4.02 \ ^oC$,calculate the value of $x$. Given $k_f \ (H_2O) = 1.86 \ K \ kg \ mol^{-1}$.

The freezing point of a $5\%$ (by mass) solution of cane sugar in water is $271 \, K$. If the freezing point of pure water is $273.15 \, K$,the freezing point of a $5\%$ (by mass) solution of glucose in water will be .......... $K$.

$6 \ g$ of a non-volatile,non-electrolyte $X$ dissolved in $100 \ g$ of water freezes at $-0.93^{\circ} C$. The molar mass of $X$ in $g \ mol^{-1}$ is ($K_f$ of $H_2O = 1.86 \ K \ kg \ mol^{-1}$)

How does sprinkling of salt help in clearing the snow-covered roads in hilly areas? Explain the phenomenon involved in the process.