Oxygen is the gas essential for combustion. It plays a crucial role in the chemical reaction that occurs during burning. When a substance, such as wood or gasoline, ignites, it reacts with oxygen from the air. This reaction produces heat and light, resulting in fire. The more oxygen that is available, the more efficiently combustion can occur. In a controlled environment, such as a combustion engine, managing the amount of oxygen is essential for optimal performance. Without sufficient oxygen, combustion is incomplete, leading to smoke and other byproducts instead of a clean burn.