Q. Assertion : The molecular weight of acetic acid determined by depression in freezing point method in benzene and water was found to be different.
Reason : Water is polar and benzene is non-polar.

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Solution:

In benzene acetic acid dimerises but in water it does not. This is because benzene is non-polar whereas water is polar.
The number of particles become different in both the solvents. Depression in freezing point is a colligative property i.e., it depends upon the number of particles in solution. Hence, molecular mass determined by depression in freezing point method comes out to be different (They have different depression in freezing point.