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.