Elemental analysis of crude petroleum: choose the approximate mass percentage of carbon typically found in untreated crude oil samples, recognizing normal assay ranges for world crudes.

Introduction / Context:
Crude petroleum is a complex mixture predominantly of hydrocarbons. Bulk elemental composition provides a fast sense of fuel properties and conversion behavior. This question focuses on the typical carbon mass percent for crude oils.

Given Data / Assumptions:

• Representative world crudes (light to heavy).
• Standard ultimate analysis of untreated crude.
• Minor heteroatoms (S, N, O, metals) present in small percentages.

Concept / Approach:
Crude oils commonly exhibit carbon in the mid-80s by weight, hydrogen around the low to mid teens, and the remainder as sulphur, nitrogen, oxygen, and trace metals. While there is variation (paraffinic vs naphthenic vs aromatic), the 85 percent by mass figure is an accepted approximate benchmark for educational problems.

Step-by-Step Solution:

Verification / Alternative check:
Published assays for benchmark crudes (e.g., Brent, WTI, Arab Light) report carbon shares in the mid-80s percent by weight with modest variation.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming a single number is exact; in practice, composition depends on crude origin and assay method, but the mid-80s figure is standard for quick estimates.

Final Answer:
85