A chemical process in which a substance reacts with oxygen to give off heat is called combustion.
Unsaturated carbon compound:
Unsaturated hydrocarbons are organic compounds that consist of carbon and hydrogen atoms with a double or a triple bond between two adjacent carbon atoms.
Examples of unsaturated carbon compounds are alkenes as well as alkynes.
Unsaturated carbon compounds give a flame with unburnt or partially burnt carbon particles as they do not burn completely.
Such a flame is yellow in color with lots of black soot which is very polluting.
Unsaturated carbon compounds on combustion give a yellow sooty flame.