Which of the following statement is incorrect regarding positive deviation from ideal behaviour

Options

A. Force of interaction decreases
B. Volume increases
C. Observed vapour pressure is more than expected vapour pressure
D. Gibbs energy change `(DeltaG)` is positive

Answer

To determine which statement is incorrect regarding positive deviation from ideal behavior, we need to understand the characteristics of positive deviation in solutions.

### Step-by-Step Solution:

1. **Understanding Positive Deviation**:
- In a solution, positive deviation from ideal behavior occurs when the vapor pressure of the solution is greater than what is predicted by Raoult's Law. This typically happens when the interactions between the solute and solvent are weaker than the interactions between the solvent molecules themselves.

2. **Analyzing the Statements**:
- **Option A**: "The forces of attraction between solute and solvent are weak."
- This statement is correct. In positive deviation, the solute-solvent interactions are weaker than solvent-solvent interactions.

- **Option B**: "The expected vapor pressure is less than the observed vapor pressure."
- This statement is incorrect. In positive deviation, the expected vapor pressure (according to Raoult's Law) is less than the observed vapor pressure, which is a defining characteristic of positive deviation.

- **Option C**: "The volume of the mixture is greater than the sum of the volumes of the components."
- This statement is correct. In positive deviation, the total volume of the mixture is greater than the sum of the volumes of the pure components due to the weak interactions.

- **Option D**: "The Gibbs energy change (ΔG) is positive."
- This statement is misleading. While ΔG can be positive or negative depending on the specific process, there is no definitive statement about ΔG in the context of positive deviation from ideal behavior.

3. **Identifying the Incorrect Statement**:
- Based on the analysis, **Option B** is the incorrect statement regarding positive deviation from ideal behavior.

### Final Answer:
The incorrect statement regarding positive deviation from ideal behavior is **Option B**: "The expected vapor pressure is less than the observed vapor pressure."