Pure water freezes at 273 K and 1 bar. The addition of 34.5 g of ethanol to 500 g of water changes the freezing point of the solution. Use the freezing point depression constant of water as 2 K `kg mol^(-1).` The figures shown below represent plots of vapour pressure (V.P.) versus temperature (T). [molecular weight of ethanol is` 46 g mol^(-1)` Among the following, the option representing change in the freezing point is

Options

A.
B.
C.
D.

Answer

A

Explanation

As T increases, V.P. increases. Hence, option (c) and (d) are wrong.
`DeltaT_(f)=K_(f)xxm`
`Delta_(f)^(@)-T_(f)=2xx(34.5//46)/(0.5)`
`273-T_(f)=3 or T_(f)=270`.
Hence, only option (a) is correct.