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

Options

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

Answer

B

Explanation

`DeltaT_(b)=K_(b)xxm therefore0.18=0.512xxm`
`or m = 0.18//0,512`
`DeltaT_(f)=K_(f)xxm=1.86xx(0.18)/(0.512)=0.654`
`therefore" "T_(f)=-0.654^(@)C`