During fractional distillation, why do fractions contain molecules with a similar number of carbon atoms?

The correct option is Because they have similar boiling points.

The correct option is Because they have similar boiling points. Because they have similar boiling points is correct because it directly supports the approved learning objective to explain that crude oil hydrocarbons may be separated into fractions by fractional distillation. This belongs to Fractional distillation and petrochemicals within Carbon compounds as fuels and feedstock, so the answer must use the correct organic chemistry context. The other options are incorrect when they confuse the organic family, formula type, reaction condition, product, or property being tested. Keep molecular formula, structural formula, displayed formula, and general formula distinct. Do not confuse alkanes with alkenes, saturated with unsaturated, cracking with combustion, polymers with monomers, or hydrocarbons with oxygen-containing alcohols and carboxylic acids. When formulae are used, preserve the stored notation exactly and explain the GCSE chemistry idea in words rather than using unsupported displayed-formula diagrams.