C3H8 + 2O2 → 3C + 4H2O is an example of which reaction type?

• A. Addition
• B. Complete Combustion
• C. Incomplete Combustion
• D. Substitution

Answer: (C)

Incomplete combustion happens when a hydrocarbon burns with not enough oxygen, so the carbon in the fuel isn’t fully oxidized to carbon dioxide and a solid carbon (soot) can be produced along with water. In this equation, propane reacts with only two O2 molecules to give solid carbon and water. The presence of solid carbon as a product shows that there wasn’t enough oxygen to form CO2, which is what complete combustion would produce. It’s not an addition or substitution reaction, since there’s no simple adding to a double bond or replacing hydrogens with another atom; it’s a combustion process limited by oxygen supply, hence incomplete combustion.