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

Answer

D

Explanation

`DeltaT_(b)=0.18 , DeltaT_(b)=mK_(b)`
`(0.18)/(DeltaT_(f))=(mK_(b))/(mK_(f)),(0.18xx1.86)/(0.512)=DeltaT_(f),DeltaT_(f)=0.653`
`T^(0)-T_(s)=0.653, T_(s)=0-0.653^(@)C,TT_(s)=-0.653^(@)C`