Identify the component class that is desirable in petrol (gasoline) for high octane but undesirable in kerosene because it depresses smoke point: paraffins, aromatics, mercaptans, or naphthenic acid.

Introduction / Context:
Fuel performance metrics differ between gasoline and kerosene. Gasoline prioritizes octane rating to prevent knock in spark-ignition engines, while kerosene emphasizes clean burning and high smoke point for lamps and turbine/household uses.

Given Data / Assumptions:

• Gasoline requires high octane (aromatics are beneficial).
• Kerosene quality is penalized by aromatics due to soot/smoke.
• Other species (mercaptans, acids) also impact quality but differently.

Concept / Approach:
Aromatics raise octane in gasoline because of their low tendency to autoignite under SI conditions. Conversely, aromatics reduce smoke point and worsen burning quality in kerosene, making them undesirable for that pool. Thus, the same class has opposite desirability across the two fuels.

Step-by-Step Solution:

Verification / Alternative check:
Specification trends show gasoline octane responds to aromatics content, while kerosene smoke point specifications demand lower aromatics.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming one fuel’s desirable trait automatically applies to all fuels; performance criteria differ.

Final Answer:
Aromatics