2.0g of a non-electrolyte dissolved in 100g of benzene lowers the freezing point of benzene by 1.2K. The freezing pont depression constant of benzene is 5.12 K kg `mol^(-1)`. The molar mass of the solute is

Options

A. `55g mol^(-1)`
B. `85 g mol^(-1)`
C. `120 g mol^(-1)`
D. `155 g mol^(-1)`

Answer

B

Explanation

`DeltaT_(f) = K_(f) m = K_(f) xx (W_(2))/(M_(2)) xx (1000)/(w_(1))`
`1.2 = (5.12 xx 2 xx 1000)/(M_(2) xx 100)`
`M_(2) = 85 g mol^(-1)`