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

  1. A. made of saturated hydrocarbons.
  2. B. made of unsaturated hydrocarbons.
  3. C. burning completely.
  4. D. wet.

Correct Answer: B. made of unsaturated hydrocarbons.

Explanation

Unsaturated hydrocarbons generally exhibit a yellow, sooty flame due to incomplete combustion resulting from a higher percentage of carbon.

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