Select the correct statement about how hydrocarbon structure influences the octane number of gasoline-range fuels.

Introduction:
Octane number measures knock resistance in spark-ignition engines. Molecular structure, especially branching and aromaticity, has a strong effect on octane values, guiding reforming, isomerization, and blending strategies in refineries.

Given Data / Assumptions:

• Focus is on gasoline-range hydrocarbons (roughly C5–C10).
• Comparisons are at equal carbon numbers unless stated otherwise.
• Octane trends: branching ↑ octane, straight chains ↓ octane, aromatics often high RON.

Concept / Approach:
Branched isomers disrupt chain autoignition pathways, raising octane. Straight-chain paraffins (e.g., n-heptane with ON = 0 by definition) tend to knock readily. Iso-octane (2,2,4-trimethylpentane) defines 100 on the primary reference scale.

Step-by-Step Solution:
1) Recall reference fuels: n-heptane (0), iso-octane (100).2) Branching increases octane versus straight chains at same carbon number.3) Select the statement that correctly captures this structural effect.

Verification / Alternative check:
Isomerization units exist precisely to convert normal paraffins to branched paraffins to boost octane in reformulated gasoline blends.

Why Other Options Are Wrong:
a: Iso-octane is 100, not zero.b: Octane does not monotonically track only carbon number.d: Aromatics typically have high octane relative to naphthenes/paraffins.e: Opposite of reality; straight chains are lowest among isomers.

Common Pitfalls:
Confusing RON/MON specifics with the broader structural trends; both agree that branching improves knock resistance relative to straight-chain isomers.

Final Answer:
Branched-chain paraffins have higher octane than straight-chain paraffins of the same carbon number.