Among the listed fractions, which has the highest boiling point?

Among the listed fractions, which has the highest boiling point?

• A. Refinery gases
• B. Gasoline
• C. Kerosene
• D. Bitumen

Answer: (D)

Boiling point in hydrocarbon fractions rises with molecular size and chain length. Lighter fractions have very small molecules, so they vaporize at low temperatures. Bitumen, by contrast, consists of extremely long carbon chains and very large molecules, which leads to strong dispersion forces and a much higher energy required to vaporize. Gasoline and kerosene sit between these extremes, having longer chains than refinery gases but shorter than bitumen, so their boiling points are lower than bitumen’s. Hence, bitumen has the highest boiling point among the options.

Boiling point in hydrocarbon fractions rises with molecular size and chain length. Lighter fractions have very small molecules, so they vaporize at low temperatures. Bitumen, by contrast, consists of extremely long carbon chains and very large molecules, which leads to strong dispersion forces and a much higher energy required to vaporize. Gasoline and kerosene sit between these extremes, having longer chains than refinery gases but shorter than bitumen, so their boiling points are lower than bitumen’s. Hence, bitumen has the highest boiling point among the options.