In a 0.2 molal aqueous solution of a week acid HX, the degree of ionisation 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. `-0.260^(@)C`
C. `+0.480^(@)C`
D. `-0.481^(@)C`

Answer

d

Explanation

`{:(,HX, hArr,H^(+),+,X^(-)),("Initially",1 mol,,0,,0),("After dissociation",1-0.3,,0.3,,0.3):}`
Total moles `= 1 - 0.3 + 0.3 + 0.3 = 1.3`
`I = (1.3)/(1) = 1.3`
`DeltaT_(f) = iK_(f)M = 1.3xx1.85xx0.2 = 0.481^(@)C`