In a 0.2 molal aqueous solution of a weak acid HX the degree of ionization is 0.3. Taking `K_(f)` for water as 1.85, the freezing point of the solution will be nearest to

Options

A. `- 0.360^(@)C`
B. `0.206^(@)C`
C. `+0.480^(@)C`
D. `-0.480^(@)C`

Answer

D

Explanation

`underset("m(1-alpha)")(HX) hArr underset(m" "alpha)(H^(+)) + underset(m" "alpha)(X^(-))`
Total molality = ` m(1-alpha) + m alpha + m alpha = m ( 1+alpha)`
` Delta T_(f) = K_(f) m (1 + alpha)`
` =1.86 xx 0.2 xx (1+0.3) = 0.48^(@)`C