Petroleum chemistry: What best describes olefins (alkenes) in the context of crude petroleum and refining?

Introduction:
Olefins (alkenes) are a key class of hydrocarbons in refining reactions and gasoline quality, but their definition and typical occurrence in crude petroleum can be misunderstood.

Given Data / Assumptions:

• We compare structural class (saturation, cyclicity).
• We consider whether olefins occur substantially in raw crude.

Concept / Approach:
Olefins are unsaturated hydrocarbons with at least one C=C double bond. They are generally acyclic (though cyclic alkenes exist), and in petroleum operations they are typically generated during thermal or catalytic cracking rather than being abundant in untreated crude.

Step-by-Step Solution:

Verification / Alternative check:
Refining processes (thermal/catalytic cracking, FCC) generate olefins which influence gasoline octane and stability; raw crude assays rarely report high native olefin content.

Why Other Options Are Wrong:

• A: Saturated is wrong; olefins are unsaturated.
• B: Overstates cyclic forms; contextually misleading.
• C: Overstates crude olefin content.
• E: While generally true as a statement, it is not among the original A–D choices for a single-correct MCQ; thus the keyed answer remains D.

Common Pitfalls:
Assuming “unsaturated” automatically implies “present in crude.”

Final Answer:
None of these.