How is combustion defined?

• A. A chemical process of oxidation that occurs at a rate fast enough to produce heat and usually light in the form of either a glow or a flame
• B. A physical change in which a material changes state
• C. A biological process of energy release through metabolism
• D. A chemical process of hydration or dissolution

Answer: (A)

Combustion is a chemical reaction in which a fuel reacts with an oxidizer, usually oxygen in air, releasing heat and often light. The reaction must proceed rapidly enough to sustain heat, leading to ignition and the visible flame or glow. This rapid oxidation is what sets combustion apart from slower or non-oxidation processes. It’s not a physical change like a change of state, nor a biological metabolism, nor a hydration or dissolution process. In fire contexts, the fire triangle—heat, fuel, and oxygen—must all be present to sustain combustion. Depending on how completely the fuel oxidizes, you get different products, with complete combustion producing carbon dioxide and water, and incomplete combustion potentially producing carbon monoxide or soot.