Explanation:Hydrocarbon fuel is the fuel that is derived from a hydrocarbon, which includes gasoline and jet fuel.Unsaturated hydrocarbons give a yellow flame with lots of black smoke while saturated hydrocarbons give a clean flame.Unsaturated hydrocarbons are hydrocarbons that have double or triple covalent bonds between adjacent carbon atoms.The colour of the flame is yellow because of the presence of unburnt carbon particles.Thus, On burning hydrocarbon fuels, we see a yellow flame with lots of black smoke, which indicates that the fuel is made of unsaturated hydrocarbons.Additional InformationSaturated hydrocarbon is a hydrocarbon in which all the carbon-carbon bonds are single bonds.