While burning hydrocarbon fuels, if we see a yellow flame with lots of

While burning hydrocarbon fuels, if we see a yellow flame with lots of black smoke, it means that the fuel is :

made of saturated hydrocarbons.

made of unsaturated hydrocarbons.

burning completely.

wet.

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Answer is Wrong!

This question was previously asked in

UPSC CDS-1 – 2022

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A yellow flame with lots of black smoke indicates incomplete combustion. This occurs when there is insufficient oxygen for the fuel to burn completely. Unsaturated hydrocarbons, which have a higher carbon-to-hydrogen ratio than saturated hydrocarbons, tend to undergo incomplete combustion more readily and produce sooty flames (yellow flame and black smoke) when the oxygen supply is limited.

Complete combustion produces a clean, often blue, flame and primarily carbon dioxide and water. Incomplete combustion produces a yellow, luminous, and sooty flame, along with carbon monoxide and unburnt carbon particles (soot), which appear as black smoke. The likelihood of incomplete combustion depends on the fuel type and the oxygen supply.

Saturated hydrocarbons (like alkanes) typically burn with cleaner, often blue, flames compared to unsaturated hydrocarbons (like alkenes, alkynes, and aromatic hydrocarbons) which have higher carbon content and are more prone to incomplete combustion leading to sooty, yellow flames.

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