Which of the following compounds determines the octane rating of petrol?

The compound that determines the octane rating of petrol is 2,2,4-trimethylpentane, also known as iso-octane. Octane rating is a measure of a fuel's ability to resist "knocking" or detonation that can occur inside an engine, causing damage and reducing efficiency. Iso-octane has a high resistance to knocking, which makes it an ideal reference standard for determining the octane rating of petrol. A fuel with a higher percentage of iso-octane will have a higher octane rating and will be less likely to cause knocking in an engine.