A solution of urea (mol. Mass `60 g mol^(-1)`) boils of `100.18^(@)C` at one one atmospheric pressure. If `k_(f)` and `K_(b)` for water are `1.86` and `0.512 K kg mol^(-1)` respectively, the above solution will freeze at:

Options

A. `0.654 .^(@)C`
B. `-0.654.^(@)`
C. `0.302.^(@)C`
D. `-0.18^(@)C`

Explanation

`Delta T_(b)=(100.18-100).^(@)C=0.18.^(@)C`
Molality of solution `= (Delta T_(b))/(K_(b))=(0.18)/(0.512)`
`therefore Delta T_(f)=mK_(f)=0.86xx(0.18)/(0.152)=0.302`
Freezing point `= 0-0.302 rArr -0.302`