Dissociation is a process in which a compound breaks down into simpler substances, usually as a result of high temperature or other external factors. This process can be observed in various contexts, including combustion. Let's explore each option provided and explain why the correct answer is option 'D'.

a) Disintegration of combustion products at high temperature:
Combustion is a chemical reaction that occurs between a fuel and an oxidizing agent, usually oxygen, resulting in the release of heat and light. During combustion, the fuel molecules combine with oxygen to form combustion products, such as carbon dioxide, water vapor, and various other compounds depending on the fuel composition. However, at high temperatures, these combustion products can undergo dissociation, breaking down into simpler substances. For example, carbon dioxide can dissociate into carbon monoxide and oxygen, or water vapor can dissociate into hydrogen and oxygen. Therefore, dissociation can be considered as the disintegration of combustion products at high temperatures.

b) Reverse process of combustion:
While combustion is the process of a fuel reacting with an oxidizing agent to release energy, dissociation can be seen as the reverse process of combustion. In combustion, complex molecules combine to form simpler compounds, releasing energy. On the other hand, dissociation involves the breakdown of these simpler compounds into their constituent elements or smaller molecules. Therefore, dissociation can be considered as the reverse process of combustion.

c) Heat absorption process:
Dissociation is often an endothermic process, meaning it requires the absorption of heat energy. When molecules dissociate, bonds between atoms are broken, and this requires energy input. The absorbed heat energy provides the activation energy needed to break these bonds. Therefore, dissociation can be considered as a heat absorption process.

Given the explanations above, it is clear that all the options mentioned (a, b, and c) are correct. Dissociation involves the disintegration of combustion products at high temperature, it is the reverse process of combustion, and it is a heat absorption process. Hence, the correct answer is option 'D' - all of the above.