A`0.2` molal aqueous solution of a week acid (HX) is 20 % ionised,The frrezing point of this solution is (Given `k_(f)=1.86^(@)Ckg mol^(-1)` for water) :

Options

A. `-0.31^(@)C`
B. `-0.45^(@)C`
C. `-0.53^(@)C`
D. `-0.90^(@)C`

Answer

B

Explanation

`DeltaT_(f)= "Molarity" xxK_(f)xx(1+alpha)`
`alpha=0.2, "Molarity" =0.2,K_(f)=1.86`
`DeltaT_(f)=0.2xx1.2xx1.86=0.4464^(@)`
Freezing point `=-0.45^(@)C`