The mixture that forms maximum boiling azeotrope is :

Options

A. Heptane + Octane
B. Water + Nitric acid
C. Ethanol + Water
D. Acetone + Carbon disulphide

Explanation

To determine which mixture forms a maximum boiling azeotrope, we need to understand the concept of azeotropes and their relation to Raoult's law.

### Step-by-Step Solution:

1. **Understanding Azeotropes**:
- Azeotropes are mixtures of two or more liquids that boil at a constant temperature and maintain the same composition in the vapor phase as in the liquid phase.
- They can be classified into two types: maximum boiling azeotropes and minimum boiling azeotropes.

2. **Maximum vs. Minimum Boiling Azeotropes**:
- Maximum boiling azeotropes occur when the mixture exhibits negative deviation from Raoult's law. This means that the vapor pressure of the mixture is lower than expected, leading to a higher boiling point than that of either component.
- Minimum boiling azeotropes occur when there is a positive deviation from Raoult's law, resulting in a lower boiling point than either component.

3. **Analyzing the Options**:
- **Option A: Hexane + Octane**: This is an ideal solution and does not form an azeotrope.
- **Option B: Water + Nitric Acid (HNO3)**: This mixture shows non-ideal behavior and forms a maximum boiling azeotrope, as it exhibits negative deviation from Raoult's law.
- **Option C: Ethanol + Water**: This mixture forms a minimum boiling azeotrope due to hydrogen bonding, showing positive deviation from Raoult's law.
- **Option D: Acetone + Carbon Disulfide (CS2)**: This mixture also forms a minimum boiling azeotrope with positive deviation from Raoult's law.

4. **Conclusion**:
- Among the options, only **Option B (Water + Nitric Acid)** forms a maximum boiling azeotrope.

### Final Answer:
The mixture that forms a maximum boiling azeotrope is **Water + Nitric Acid (HNO3)**.