Consider dilute solutions of non-volatile non-electrolytes in a given solvent. Which of the following statements is/are correct?

AAt the normal boiling point of the pure solvent, the vapour pressure of the solution is less than $1 atm$ .
BSolutions of different non-electrolytes having the same molality show the same elevation of boiling point.
CThe freezing point depression depends on the molarity of the solute but not on the mass of the solvent used.
DDoubling the mass of solute dissolved in a fixed mass of solvent doubles $Δ T_{b}$ .

Answer: A, B, D

Colligative properties of dilute solutions depend on the number of solute particles per kg of solvent:

Δ T_{b} = K_{b} m

, so equal molality gives equal

Δ T_{b}

and doubling the solute mass doubles

m

. The solution's vapour pressure is lowered, so at the solvent's normal boiling point it is below

1 atm

. Freezing point depression depends on molality, which does involve the mass of solvent, so the last statement is wrong.