Hydrocarbon class with poorest oxidation stability

Introduction / Context:
Oxidation stability affects storage gum formation, varnish, and engine deposit tendencies. Different hydrocarbon classes (paraffins, naphthenes, aromatics, olefins) vary notably in susceptibility to autoxidation.

Given Data / Assumptions:

• Comparison is among the common classes in refinery products.

Concept / Approach:
Olefins contain carbon–carbon double bonds that are highly reactive toward oxygen, forming peroxides and initiating polymerization leading to gums. Saturated paraffins and naphthenes are more stable; aromatics are resonance-stabilized. Thus, olefins exhibit the poorest oxidation stability, consistent with gasoline storage concerns where unsaturates drive gum formation.

Step-by-Step Solution:

Verification / Alternative check:
Induction period tests and gum tests show faster degradation for olefin-rich fuels.

Why Other Options Are Wrong:

• Paraffins/naphthenes are saturated and comparatively resistant.
• Aromatics resist autoxidation better than olefins despite soot propensity.

Common Pitfalls:
Confusing oxidation stability (chemical) with smoke/soot tendency (combustion). Aromatics smoke more but oxidize slower than olefins in storage.

Final Answer:
Olefins