A solution of urea ( mol. `=56` g `"mol"^(-1)` ) boils at `100.18^(@)C` at the atmospheric pressure. If `K_(f)` and `K_(b)` for water are 1.86 and 0.512 K kg `"mol"^(-1)` respectively, then the above solution will freeze at :

Options

A. `0.654^(@)C`
B. `-0.654^(@)C`
C. `6.54^(@)C`
D. `-6.54^(@)C`

Answer

B

Explanation

`m=(DeltaT_(f))/(K_(f))=(Delta T_(b))/(K_(b))`
`Delta T_(b)=100.18-100=0.18^(@)`
`:.DeltaT_(f)=(Delta T_(b))/(K_(b))xxK_(f)`
`=(0.18)/(0.512)xx1.86=0.654^(@)`
`:.` Freezing point of solution `=0-0.654`
`=-0.654^(@)C`