What is combustion?

• A. A chemical reaction occurring when water turns into steam.
• B. A chemical reaction between a fuel and an oxidizing agent, usually oxygen, that releases energy as heat and light.
• C. A physical change where substances mix without reacting.
• D. A reaction that only happens in the presence of a catalyst.

Answer: (B)

Combustion is a chemical reaction in which a fuel reacts with an oxidizer, usually oxygen from the air, and energy is released as heat and light. This reaction transforms the reactants into new substances, typically producing carbon dioxide and water when fossil fuels burn. The key points are that it involves a chemical change, requires an oxidizer, and releases energy that often appears as heat and a visible flame. This distinguishes it from a phase change like water turning into steam, which is not a chemical reaction; from simply mixing substances without reacting; and from reactions that need a catalyst, which combustion does not inherently require.