Gasoline quality additives: Which of the following is commonly used as an antiknock additive or blending component that improves octane in spark-ignition fuels?

Introduction / Context:
Antiknock quality (octane number) measures a fuel’s resistance to auto-ignition under spark-ignition conditions. Refiners and blenders use components with high octane to improve gasoline performance and meet regulatory standards.

Given Data / Assumptions:

• Focus is on SI engine antiknock improvement (octane).
• Historically, tetraethyl lead was used; modern practice includes oxygenates like ethanol.
• We choose among the listed species.

Concept / Approach:
Alcohols such as ethanol possess high blending octane numbers and act as oxygenates that can raise the octane of gasoline pools. Mercaptans are odourants (not antiknock agents). Pyridine is a nitrogenated base chemical, not used for octane improvement. Amyl nitrate is known as a diesel ignition improver (cetane improver), which has the opposite goal—reducing ignition delay—not the antiknock role in gasoline.

Step-by-Step Solution:

Verification / Alternative check:
Fuel standards and blending guides cite ethanol’s high RON/MON and widespread use as an octane enhancer and oxygenate.

Why Other Options Are Wrong:

Common Pitfalls:
Mixing up octane improvers (SI engines) with cetane improvers (CI engines); they aim at opposite ignition behaviours.

Final Answer:
Alcohols (e.g., ethanol)