2022 · Q11
While burning hydrocarbon fuels, if we see a yellow flame with lots of black smoke, it means that the fuel is:
General KnowledgeChemistry
- Amade of saturated hydrocarbons
- Bmade of unsaturated hydrocarbons
- Cburning completely
- Dwet
Explanation
Unsaturated hydrocarbons (e.g., ethyne) burn with a luminous yellow flame and release black smoke (soot) because combustion is incomplete — unburnt carbon particles escape. Saturated hydrocarbons burn cleanly with a blue, non-sooty flame. A yellow, smoky flame therefore indicates an unsaturated fuel burning incompletely.