After adding non-volatile solute, freezing point of water decreases to `-0.186^(@)C`. Calculate `Delta T_(b)` if :
`K_(f) = 1.86 "K kg mol"^(-1) and K_(b) = 0.521 "K kg mol"^(-1)`

Options

A. `0.512`
B. `0.0521`
C. `1.86`
D. `0.0186`

Answer

B

Explanation

Accprding to Raoult's law, when a non-volatile solute is added to the solvent its vapour pressure decreases and now its vapour pressure would become equal to that of solid solvent at lower temperature. ltbr gt The freezing point of the solvent decreases.
`DeltaT_(f)propm(m=" molality of solution"`
`DeltaT_(f)=K_(f)m,0.186=1.86xxm`
`:.m=0.1`
Now `DeltaT_(b)=K_(b)xxm=0.521xx0.1=0.0521`