Combustion:
Combustion is a chemical reaction that occurs between a fuel and an oxidizing agent, resulting in the release of heat and light. It is a common process that takes place in various forms, such as burning wood, lighting a candle, or igniting gasoline in a car engine. Combustion is an exothermic reaction, meaning it releases energy in the form of heat.

Flame:
A flame is the visible, gaseous part of a fire. It is the result of combustion, where the fuel and oxidizing agent react to produce heat, light, and various combustion products. Flames can vary in size, color, and intensity depending on the type of fuel and oxidizing agent involved.

Differences between Combustion and Flame:

1. Definition:
- Combustion: Combustion is a chemical reaction between a fuel and an oxidizing agent that releases heat and light.
- Flame: A flame is the visible, gaseous part of a fire resulting from combustion.

2. Nature:
- Combustion: Combustion is a chemical reaction that involves the breaking and forming of chemical bonds.
- Flame: A flame is the visible part of the combustion process, where the released energy is manifested as heat and light.

3. Presence:
- Combustion: Combustion can occur without the presence of a visible flame, such as in internal combustion engines or industrial furnaces.
- Flame: A flame is the visible part of the combustion process and is present when there is sufficient heat and the right conditions for ignition.

4. Appearance:
- Combustion: Combustion may or may not have a visible flame. It can be a slow, smoldering process without a distinct flame.
- Flame: A flame is the glowing, luminous gas that is visible during combustion. It has a distinct shape and emits light and heat.

5. Role:
- Combustion: Combustion is the chemical reaction that releases energy in the form of heat and light.
- Flame: A flame is the visible manifestation of the energy released during combustion.

6. Products:
- Combustion: Combustion produces combustion products, such as carbon dioxide, water vapor, and various pollutants depending on the fuel and oxidizing agent.
- Flame: A flame is primarily composed of hot gases, including unburned fuel, combustion products, and ionized particles.

In summary, combustion is the chemical reaction that releases heat and light, while a flame is the visible part of the combustion process. Combustion can occur without a visible flame, but a flame is always present when there is sufficient heat and the right conditions for ignition.