Concept:Octane rating is measured against a standard reference fuel called iso-octane, which is assigned a rating of 100.Explanation:The IUPAC name of iso-octane is 2,2,4-trimethylpentane.This compound is chosen as the standard because it produces very little knocking in an engine.Therefore, the compound that determines the octane rating of petrol is 2,2,4-trimethylpentane.Among the listed options, this compound matches option D.Answer:D. 2,2,4-trimethylpentane