Concept:Incomplete combustion of petrol causes unburnt carbon particles to deposit in exhaust pipes.
Explanation:Petrol is a hydrocarbon fuel that should burn completely in oxygen.
Complete combustion would produce only carbon dioxide,
CO2, and water vapour.
However, inside a car engine, oxygen supply is often limited or mixing is imperfect.
This leads to incomplete combustion of petrol.
The unburnt carbon separates as fine soot particles.
These particles are carried along with the exhaust gases and get deposited inside the exhaust pipes.
Therefore, the deposition of carbon is due to incomplete combustion of petrol.
Answer:B. Incomplete combustion of petrol