What is the difference between a complete and incomplete combustion reaction?

Hint: A combustion reaction is a chemical reaction in which a fuel is oxidised and energy is released. Exothermic reactions are chemical processes in which energy is released. As a result, combustion processes are exothermic in nature. An oxidising agent can be used to oxidise a fuel. Most combustion processes use ambient oxygen as an oxidising agent. Combustion processes can produce either heat or light as a result of the energy released. Heat is the most common form of energy release, however light energy may also be produced in the form of a flame.

Complete answer:
Complete combustion-
The full oxidation of fuel is known as complete combustion. This reaction is extremely exothermic, meaning it produces a lot of energy but just a few products. Hydrocarbons in the fuel are oxidised by ambient oxygen during combustion, producing carbon dioxide and water as byproducts. When there is a sufficient amount of oxygen available, full combustion occurs. Carbon atoms in hydrocarbons can be oxidised to carbon dioxide and hydrogen to water in the presence of oxygen. The following is a general response for full combustion.
 $ \text{Hydrocarbon }\text{ + Oxygen}\to \text{ }\text{ Carbon dioxide }\text{ + Water} $
 $ {{C}_{2}}{{H}_{5}}O{{H}_{(l)}}~~~~~~~\text{ }+~~~~\text{ }3{{O}_{2(g)}}~~~~~~~~~~~\text{ }\to ~~\text{ }~~~~~~~~~~~2C{{O}_{2(g)}}~~~~~\text{ }+~~~~\text{ }3{{H}_{2}}{{O}_{(l)}} $
Complete combustion produces carbon, sulphur, and other elements contained in the fuel as oxides. Sulfur is oxidised to sulphur dioxide whereas carbon is converted to carbon dioxide. Complete combustion produces less pollutants in the air. A blue flame can be seen after full combustion has occurred.

Incomplete combustion-
Incomplete combustion is a chemical process in which only a portion of the fuel is oxidised. When there isn't enough oxygen in the air, incomplete combustion happens. Fuel is only partially oxidised here. As a result, incomplete combustion produces a variety of byproducts. However, the quantity of energy released by this combustion is rather little. Carbon monoxide and water are the main byproducts of incomplete combustion. The incomplete combustion formula is.
The byproducts may differ depending on how much oxygen is used in the combustion. For example, it can occasionally just produce carbon monoxide or soot. However, it frequently produces a combination of carbon monoxide, soot, and water.
 $ \text{Hydrocarbon }\text{ }\text{ + }\text{ }\text{ }\text{ }\text{ Oxygen }\text{ }\text{ }\text{ }\text{ }\text{ }\text{ }\text{ }\text{ }\text{ }\to \text{ }\text{ }\text{ }\text{ }\text{ }\text{ }\text{ }\text{ Carbon monoxide }\text{ }\text{ }\text{ + }\text{ }\text{ }\text{ Carbon }\text{ }\text{ }\text{ }\text{ + }\text{ }\text{ }\text{ Water} $
 $ {{C}_{2}}{{H}_{5}}O{{H}_{(l)}}~~~~\text{ }+~~~~\text{ }2{{O}_{2(g)}}~~~~\text{ }\to ~~~\text{ }2C{{O}_{(g)}}~~~\text{ }+~~~\text{ }3{{H}_{2}}{{O}_{(l)}} $

Note:
There are two types of combustion: full combustion and partial combustion. Complete combustion differs from incomplete combustion in that carbon dioxide is the sole result that contains carbon, whereas incomplete combustion produces carbon monoxide and carbon dust as products.