0.2 molal aqueous solution of acid HX is 20% ionised. `K_f="1.86 K molal"^(-1)`. The freezing point of the solution is very close to:

Options

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

Answer

A

Explanation

`Delta T_(f)= K_(f)xx` molality `xx (1 + alpha)= underset(1- alpha)(HA) hArr underset(alpha)(H^(+)) + underset(alpha)(A^(-)) (alpha= 0.2)`
`Delta T_(f)= 1.86 xx 0.2 xx 1.2`
`Delta T_(f)= 0.45 therefore T_(f)= -0.45^(@)C`