The petrol, octane number of which is 80, has:A.20% n-heptane + 80% iso-octaneB.20% n-heptane + 80% n-octaneC.80% n-heptane + 20% iso-octaneD.80% n-heptane + 20% n-octane

The octane rating of petrol (gasoline) is a measure of its resistance to "knocking" or "pinging" during combustion, which can cause engine damage and reduced performance. Higher octane numbers indicate better resistance to knocking.

In this case, the petrol has an octane number of 80. The octane number is determined by comparing the performance of the fuel to a mixture of iso-octane (2,2,4-trimethylpentane) and n-heptane in a standardized test engine. The higher the percentage of iso-octane in this mixture, the higher the octane rating.

So, for a petrol with an octane number of 80, it means that it performs as well as a mixture of 80% iso-octane and 20% n-heptane in the test engine.

The correct answer is A. 20% n-heptane + 80% iso-octane.