Octane number is highest in petrol containing a high proportion of

Octane number is a measure of the performance of petrol in internal combustion engines. It is a rating based on the ability of petrol to resist 'knocking' or 'pinging' during combustion. Knocking or pinging is an undesirable condition that occurs when the air-fuel mixture in the engine's cylinder detonates prematurely, which can cause engine damage. A high octane number indicates that the petrol can resist knocking, allowing the engine to operate at higher compression ratios, which typically results in more power and efficiency. Therefore, petrol containing a high proportion of compounds with high resistance to knocking, such as 2,2,4-trimethylpentane (also known as iso-octane), will have a higher octane number. Hence, the correct option is 2,2,4-trimethylpentane.