The petrol having octane number 80 has ____________?

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20% n-heptane + 80% iso-octane - The octane number of petrol is a measure of its ability to resist knocking during combustion in an internal combustion engine. Knocking occurs when the fuel-air mixture ignites prematurely, causing engine vibrations and loss of efficiency. The octane rating system is based on comparing the fuel to a standard mixture of iso-octane (2,2,4-trimethylpentane) and n-heptane.
In this scale:


Iso-octane is assigned an octane number of 100 because it resists knocking very well.


n-Heptane is assigned an octane number of 0 because it ignites very easily, causing severe knocking.


When petrol is said to have an octane number of 80, it means that the fuel behaves the same way, in terms of knocking resistance, as a mixture containing 80% iso-octane and 20% n-heptane by volume. This is a reference standard and does not necessarily represent the actual composition of commercial petrol, but it is used to express its anti-knock quality











The other given options are incorrect because they either have the proportions reversed or mention n-octane, which is not used as a standard reference fuel in determining octane numbers.
A higher octane number indicates better fuel quality, meaning it can withstand greater compression before ignition. Fuels with higher octane ratings are important for modern, high-performance engines because they ensure smooth combustion, better efficiency, and reduced knocking.
This concept is crucial in environmental chemistry and fuel technology because using the correct octane rating reduces engine wear and harmful emissions. Understanding how octane numbers are determined helps in designing fuels that improve engine performance while minimizing environmental impact.

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The petrol having octane number 80 has ____________?

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