Solution:concept - Octane number indicates the resistance of gasoline or other petrochemical fuels to causing knocking in gasoline internal combustion engines used in automobiles and other vehicles.
Engine knocking or knocking or detonation is a process in which abnormal fuel combustion occurs out of control. Basically, knocking occurs when fuel combustion in the cylinder is not the result of the propagation of the flame front ignited by the spark plug, but rather one or more pockets of fuel explode uncontrollably in the chamber.
The octane number is a comparison between the amount of knocking caused by the fuel during combustion and the amount of knocking caused by standard reference fuels.
Standard reference fuels are isooctane, which is 2,2,4-trimethylpentane and n-heptane.
Iso-octane has the highest knock resistance and therefore has an octane rating of 100, while n-heptane has the least knock resistance, making it a poor knock fuel with a 0 octane rating.
The higher the octane number of the fuel, the higher the efficiency of the fuel.
Therefore, the octane number of isooctane is 100.
Hence, the correct option is (3).