Question

Which of the following has the highest knocking property?
A. Olefins
B. Straight-chain paraffins
C. Branched-chain paraffins
D. Aromatic hydrocarbons

Answer 1

Hint: Knocking is related to the fuel that is present in the engine of the vehicle. Premature ignition of the fuel leads to the production of a high-frequency sound from the engine cylinder. The sound produced is known as knocking.

Complete step by step answer:
Knocking refers to the sharp metallic sounds that are caused by the premature ignition of the fuel in the engine.
Knocking is a result of the rapid combustion of the ned gas before the flame front which in turn goes chemical reaction before the normal combustion
This results in high-frequency pressure oscillations inside the cylinder that produce the sharp metallic noise called knock.
One more factor that operates here is the octane number. It is a property related to petrol.
The octane number is directly proportional to the quality of petrol that is used, the higher the octane number the better is the quality of petrol and its efficiency.
High values of octane numbers are a measure of the fueling delay in auto-ignition.
The straight-chain alkanes have the minimum octane number and hence from the above points, we can confer that they produce maximum knocking.

So, the correct answer is Option B.

Note: 1. The octane number trend can be represented as
Straight chain paraffin $ < $ branched chain paraffin $ < $ Olefins $ < $ Aromatic hydrocarbons
2. Anti-knock agents are important agents which when added to the petrol fuel raises its octane number, this, in turn, increase the temperature at which the fuel will ignite automatically
It allows the fuel and air to wait until the spark plug of the vehicle ignites the fuel, which in turn reduces pre-detonation.
3. Alcohol, toluene, tetraethyl lead are typical anti-knocking agents.