Concept:Raoult's Law relates the physical properties of a solution to the concentration of a non-volatile solute dissolved within it, establishing colligative properties.
Formula:$$ \frac{\Delta P}{P^{\circ}} = X_{\text{solute}} $$
Solution:- \( \Delta P \) is the lowering of vapor pressure (\( P^{\circ} - P \)).
- Dividing by the pure solvent pressure (\( P^{\circ} \)) gives the "relative" lowering.
- Raoult experimentally proved that this fractional drop is exactly equal to the Mole fraction of the solute (\( X_{\text{solute}} \)).
- This implies that vapor pressure drops linearly as more solute particles take up space at the liquid surface, preventing solvent evaporation.
Why other options are incorrect:The mole fraction of the solvent defines the
remaining vapor pressure (\( P = P^{\circ} X_{\text{solvent}} \)), not the
lowering. Molarity and Molality are different concentration units entirely.
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