Petroleum fractions differ by chain length, boiling point, and viscosity

Steps:

• Fractional distillation separates petroleum hydrocarbons by boiling point, with lower-boiling fractions at the top.
• Kerosene/paraffin fraction boils at 150–275°C, containing C9–C16 alkanes.
• Lubricating oil fraction boils above 300°C, containing longer C20+ alkanes.
• Longer alkane chains increase viscosity through stronger van der Waals forces and molecular entanglement.

Why A is correct:

• Hydrocarbons with longer chains exhibit higher viscosity due to increased intermolecular forces, as defined in organic chemistry properties of alkanes.

Why the others are wrong:

• B: Lubricating oil boils at higher temperatures (above 300°C) than kerosene (150–275°C).
• C: This statement is actually correct, as lubricating oil has higher boiling points than kerosene.
• D: Lubricating oil contains longer-chain molecules (C20+) than kerosene (C9–C16).

Final answer: A