API gravity trend across crude fractions: Among the listed refinery cuts, which fraction typically exhibits the highest API gravity (i.e., is the lightest)?

Introduction / Context:
API gravity is an inverse density scale widely used in petroleum production and refining. Higher API indicates lower density and lighter material. Understanding API trends across fractionation cuts helps with blending and product property control.

Given Data / Assumptions:

• Fractions are ranked by normal boiling range: gasoline (lightest), diesel and gas oils (heavier), vacuum gas oil (heaviest among those listed).
• Higher boiling fractions have higher molecular weight and density.
• Typical API: gasoline often above 60, diesel around 30–40, gas oils lower.

Concept / Approach:

Atmospheric distillation separates crude into cuts. Light naphtha and gasoline-range streams have the lowest density and thus the highest API. As boiling range increases to diesel, AGO, and VGO, density rises and API falls.

Step-by-Step Solution:

Verification / Alternative check:

Crude assay data consistently show gasoline/naphtha cuts with the highest API gravity among distillates.

Why Other Options Are Wrong:

Diesel, atmospheric gas oil, vacuum gas oil: Progressively heavier, higher density, hence lower API.

Common Pitfalls:

Assuming API is a quality metric independent of density; it is solely a measure of relative density and does not directly indicate octane or cetane.

Final Answer:

Gasoline (light naphtha range)