The separation of petroleum fractions depends on the differences in their

1. Analyze the question It asks about the property that allows the fractions of petroleum (crude oil) to be separated from one another.

2. Explain the concept Crude oil is a mixture of many hydrocarbons. These are separated by fractional distillation, which works because each hydrocarbon has a different boiling point. The boiling point depends on the size of the molecule: larger molecules have stronger intermolecular (van der Waals) forces, so they boil at higher temperatures.

3. Step-by-step solution

• The crude oil is heated in a furnace until most of it vaporizes.
• The vapor enters a fractionating column, which is hotter at the bottom and cooler at the top.
• As the vapors rise, each one condenses at the level where the temperature is just below its boiling point.
• Fractions with low boiling points (refinery gas, petrol/gasoline) rise to the top. Fractions with high boiling points (diesel, lubricating oil, bitumen) condense lower down or stay at the bottom.

Checking the other options:

• A. Melting points: not used, because the process involves vaporizing and condensing, not melting.
• B. Molar masses: these do differ, but they are not the property the separation directly uses. Molar mass only influences the boiling point indirectly.
• C. Solubilities: not relevant, since no solvent is used.

4. Answer The correct option is D. boiling points.

5. Exam tip Whenever you see "fractional distillation" (petroleum, liquid air, ethanol-water mixtures), think boiling points. Remember: "Fractions are separated by boiling, not by melting or dissolving."