Question

A crystalline white solid is a mixture of glucose (C6H12O6) and sucrose (C12H22O11). Is it possible that a 10.00 g sample of the solid dissolved in 100.0 g H2O might have a freezing point of -1.25 degrees C? Explain.


Answer: No. The freezing point would be -1.03 degrees C

Answer 1

I don't think this problem can be worked exactly since there is no indication of how the mixture is divided between the two sugars. You can, however, calculate the freezing point assuming it is pure glucose and assuming it is pure sucrose. The 1.03 cited in the answer is assuming pure glucose.
mols glucose = grams/molar mass
m = mols/kg solvent
delta T = Kf*m = about =-1.03

Do the same for sucrose.
I get about -0.5.
So no matter the composition, it can't make it to -1.25.