Question

Octane number of iso-octane is:
(A) 50
(B) 25
(C) 100
(D) 150

Answer 1

Hint: Recollect what is meant by octane number. Take a look at petroleum chemistry and then try to attempt the answer. Find out the reference values and the reference standard compounds used to determine octane number to get the answer.

Complete step by step answer:
- The octane number is also known as octane rating which gives the measure of resistance of gasoline or other petrochemical fuels to cause knocking in spark-ignition internal combustion engines used in automobiles and other vehicles.
- Knocking or engine knocking or detonation is the process in which there is abnormal combustion of fuel beyond the control. Basically, knocking occurs when combustion of fuel in the cylinder does not result from propagation of the flame front ignited by the spark plug, but one or more pockets of fuel explode in the chamber uncontrollably.
- Octane number represents the comparison between the amounts of knocking a fuel causes when it undergoes combustion and the amounts of knocking caused by standard reference fuels.
- By default, the standard reference fuels used are iso-octane which is 2,2,4-trimethylpentane and n-heptane.
- Iso-octane has the highest resistance to knocking and so it has the octane number 100 whereas, n-heptane has least resistance to knocking and so, it is bad knocking fuel having octane number 0.
- Octane number is the average of MON (motor octane number) and RON (reference octane number) which are calculated with the help of a test engine.
- Higher the octane number of a fuel, more is the efficiency of the fuel.
- Therefore, the octane number of iso-octane is 100.
So, the correct answer is “Option C”.

Note: Remember octane number is the rating of anti-knocking property of a fuel. The fuel will be highly efficient if it has high resistance to knocking. Higher the octane number, higher is the efficiency of the fuel. Octane number of iso-octane is 100 and that of n-heptane is 0 and both are the standard reference fuels used in calculation of octane numbers of other fuels.