In a `0.2 m` aqueous solution of week acid, HX, the degree of ionization is `0.3.` Taking `K _(f)` for water as
`1 85 K kg "mole" ^(-1),` the freezing point of the solution will be nearest to :

Options

A. `- 0. 360 ^(@)C`
B. `- 0. 260^(@)C`
C. `+ .480^(@)C`
D. `272.52 K`

Answer

D

Explanation

Initially with 1 mol,
` {:(HX " "to " "H ^(+) " "+ " "X ^(-)), ( ( 1- 0. 3) " "0.3 " "0.3):}`
Total number of moles of all species =1. 3
so, `I = 1. 3` ( Van.t Hoff factor)
`( - Delta T _(f) ) = iK _(f). m`
`= 1. 3 xx 1. 85 xx 0. 2 = 0. 48 K`
`T_(f) = 273 - 0 . 48 = 272 . 52 K`