In a 0.2 molal aqueous solution of a weak acid HX the degree of ionisation is 0.3. Taking K, for water as `1.85^@C m^(-1)`, the freezing point of solution will be nearest to

Options

A. `- 0.480^@C`
B. `-0.360^@C`
C. `-0.260^@C`
D. `+ 0.480^@C`

Answer

D

Explanation

Initial Final .
`underset({:(1),(1-0.3):})(HX) to underset({:(1),(0.3):})H^+ + underset({:(1),(0.3):})X^-`
`f = (1-0.3 +0.3+0. 3)/1 =1.3`
`DeltaT_f= iK_f m= 1.3 xx 1.85 xx 0.2 = 0.480`
`T_f = 0 -0.480 = -0.480^@C`