Gasoline pool comparison (unleaded): Among the following gasoline types, which one generally exhibits the lowest octane number before any additional upgrading or special blending?

Introduction / Context:
Gasoline streams differ in octane due to how they are produced. Understanding which refinery stream starts with the lowest octane helps explain why upgrading units (reforming, isomerization) are essential in modern refineries.

Given Data / Assumptions:

• Unleaded context; no TEL or MMT.
• “Straight run” means naphtha directly from atmospheric distillation.
• Typical FCC gasoline and reformate qualities are considered.

Concept / Approach:
Straight run gasoline is rich in normal paraffins and light naphthenes, giving comparatively low octane. Catalytically reformed gasoline (reformate) is rich in aromatics/isoparaffins, hence high octane. Polymer gasoline and FCC gasoline contain more branched and olefinic species, typically higher octane than straight run.

Step-by-Step Solution:

Verification / Alternative check:
Refinery textbooks place reformate at the high end of octane and straight run at the low end, motivating upgrading steps.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming “cracked” gasoline is always poor quality; for octane specifically, cracked/reformed streams are superior to straight run.

Final Answer:
Straight run gasoline