Raoult’s law deviations in binary solutions:\nIf component A shows a positive deviation from Raoult’s law in an A–B liquid mixture, what deviation does component B exhibit?

Introduction / Context:
Non-ideal liquid mixtures often deviate from Raoult’s law. Understanding the sign of deviation helps predict azeotrope formation tendencies and guides separation strategies like distillation. Deviations reflect the relative strength of intermolecular interactions between unlike and like molecules.

Given Data / Assumptions:

• Binary liquid solution of components A and B.
• Component A exhibits positive deviation (higher partial pressure than ideal).

Concept / Approach:
A positive deviation implies that A–B interactions are weaker than A–A and B–B on average, leading to greater escaping tendency (higher activity) for both components. Consequently, both components typically show positive deviations. Conversely, stronger unlike interactions cause negative deviations for both components. Thus, deviation signs are paired in binary systems under standard assumptions.

Step-by-Step Solution:

Verification / Alternative check:
Phase diagrams of classic positive-deviation systems (e.g., ethanol–cyclohexane) show total pressures above ideal predictions for the entire composition range, indicating both components deviate positively.

Why Other Options Are Wrong:

• Negative or obeys Raoult: inconsistent with the symmetric effect of interaction weakening.
• Independent sign: in a simple binary with uniform interactions, deviations are not independent.
• No vapor pressure: physically incorrect for volatile liquids considered.

Common Pitfalls:
Assuming that only one component deviates; in binary solutions, deviation behavior is coupled through A–B interactions.

Final Answer:
Positive deviation from Raoult’s law.