Answer:
D. insufficient supply of oxygen
Step-by-step explanation:
Combustion is an exothermic reaction which involves the burning of a compound in the presence of oxygen. Combustion is a very useful life process as it produces heat and light.
For a complete combustion reaction to occur, the compound must be burnt over excess oxygen. The product is usually carbondioxide and water with release of some particulate matter.
In incomplete combustion, there is deficiency of oxygen. Here, oxygen becomes the limiting agent and it drives the reaction to an end. Incomplete combustion is always accompanied with the production of poisonous carbon monoxide and Carbon. We see incomplete combustion when smoke forms or when burning is accompanied by production of soot.
What makes a combustive process complete or not is the availability of oxygen gas for the reaction.