Octane number reference compound: Iso-octane is used as the 100-point reference for octane number. Its correct chemical name is:

Introduction:
Octane number compares gasoline knock resistance to a reference blend of iso-octane (defined as 100) and n-heptane (defined as 0). The question asks for the correct chemical name of iso-octane.

Given Data / Assumptions:

• Standard octane definition is implied.

Concept / Approach:
Iso-octane is the branched paraffin 2,2,4-trimethylpentane. Its high knock resistance under spark-ignition conditions makes it the 100 reference point.

Step-by-Step Solution:

Verification / Alternative check:
Fuel property tables list iso-octane explicitly as 2,2,4-trimethylpentane.

Why Other Options Are Wrong:

• α-methyl naphthalene: Aromatic; historical cetane reference, not octane.
• 1,3-butadiene / Tetramethylethylene: Olefins, not the octane standard.
• 3-ethylhexane: Another isomer, not the octane reference.

Common Pitfalls:
Mixing up octane and cetane reference compounds.

Final Answer:
2,2,4-trimethylpentane