What causes the production of carbon monoxide and soot during fuel combustion?

The production of carbon monoxide and soot during fuel combustion is primarily caused by incomplete combustion. When combustion occurs in an environment where there isn't enough oxygen to allow the fuel to react completely, it results in the formation of carbon monoxide, which is a poisonous gas, as well as soot, which is made up of fine carbon particles.

In complete combustion, there is sufficient oxygen available, resulting in the fuel being converted completely into carbon dioxide and water, without the formation of harmful byproducts like carbon monoxide or soot. High temperatures alone do not directly cause the production of these byproducts; rather, they can contribute to combustion efficiency. An excess of oxygen would further support complete combustion and reduce the potential for any form of incomplete combustion and its associated products. Therefore, the answer clearly identifies incomplete combustion as the key factor in the generation of carbon monoxide and soot.