A solution of urea (mol mass `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 `0.512K kg mol^(-1)` respectively, the above solution will freeze at,

Options

A. `-6.54^(@)C`
B. `6.54^(@)`
C. `0.65^(@)C`
D. `-0.654^(@)C`

Answer

D

Explanation

`Delta T_(b) = 100.18-100=0.18`
`(Delta T_(b))/(Delta T_(f)) = (K_(b)m)/(K_(f)m)=(K_(b))/(K_(f))`
`(0.18)/(Delta T_(f)) = (0.512)/(1.86)`
`Delta T_(f) = (0.18xx1.86)/(0.512)=0.654`
`T_(f)=(0-0.654)^(@)C=-0.654`