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

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Q: 11 (CDS-I/2022)
While burning hydrocarbon fuels, if we see a yellow flame with lots of black smoke, it means that the fuel is :

question_subject: 

Science

question_exam: 

CDS-I

stats: 

0,207,99,56,207,15,28

keywords: 

{'yellow flame': [0, 0, 0, 1], 'hydrocarbon fuels': [0, 0, 0, 1], 'black smoke': [0, 0, 0, 1], 'unsaturated hydrocarbons': [0, 0, 0, 1], 'hydrocarbons': [1, 0, 2, 5], 'fuel': [1, 0, 5, 14]}

When burning hydrocarbon fuels, the color of the flame and the amount of smoke produced can provide important information about the composition and efficiency of the fuel. In this case, a yellow flame with lots of black smoke indicates that the fuel is made of unsaturated hydrocarbons.

Option 1: Saturated hydrocarbons typically produce a blue flame when burning. A yellow flame suggests the presence of impurities or incomplete combustion.

Option 3: A complete combustion of hydrocarbon fuels would produce a blue flame with minimal smoke. The presence of a yellow flame and black smoke indicates that the fuel is not burning completely.

Option 4: The presence of water in the fuel would generally not affect the color of the flame or the amount of smoke produced.

Therefore, option 2 is the correct answer as a yellow flame with black smoke indicates the burning of hydrocarbon fuels made of unsaturated hydrocarbons.