Depression in freezing point (Δ
) = 
×m×i,
where, = cryoscopic constant = 
,
m= molality of solution = 0.0085 m
i = van't Hoff factor = 2 (For
)
Thus, (Δ) = 1.86 X 0.0085 X 2 = 
Now, (Δ) = 
- T
Here, T = freezing point of solution
= freezing point of solvent = 
Thus, T = - (Δ) = -
where,
m= molality of solution = 0.0085 m
i = van't Hoff factor = 2 (For
Thus, (Δ
Now, (Δ
Here, T = freezing point of solution
Thus, T =