How many grams of methyl alcohol should be added to 10 L tank of water to prevent its freezing at 268 K?

Normal freezing point of water = 273.15 K. In order to  prevent freezing at 268 K, let the amount of methanol added be x g.∴       Molality, m =x32×10=x320[∵ Molar mass of CH3OH=32 g mol-1and volume of H2O =10 L]Now,                ∆Tf=Kf.m    273.15-268=1.86×x3205.15=1.86×x320∵Kf for water =1.86 K kg mol-1 or     x=5.15×3201.86=886.02 g