What type of reaction involves a complex molecule breaking down into simpler substances?

The correct answer is a decomposition reaction, which is defined as a type of chemical reaction where a complex molecule is broken down into simpler substances. This process typically occurs when a single compound is broken down into two or more simpler products, usually as a result of the input of energy, such as heat, light, or electricity.

In a decomposition reaction, the bonds holding the various atoms and molecules together are broken, leading to the formation of simpler molecules or elements. A common example of a decomposition reaction is the breakdown of water (H2O) into hydrogen (H2) and oxygen (O2) gas through electrolysis.

Understanding this type of reaction is essential as it plays a crucial role in various chemical processes, including the breakdown of organic matter and the digestion of food in biological systems. Recognizing decomposition reactions helps link concepts of chemical change and energy transformation, illustrating the nature of chemical reactivity.