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. `-0.260^@C`
C. `+0.481^@C`
D. `-0.481^@C`

Answer

D

Explanation

`(underset("1-0.3")(HX) hArrunderset(0.3)overset(+)H + underset(0.3)X^(-), i= 1.3), DeltaT_f = K_f xxm xxi`
`DeltaT_f = 1.85 xx 0.2xx 1.3 = 0.481 ^@C`
`:. T_f=T_f^@-DeltaT_f = 0-0.481^@C = -0.481^@C`