What characterizes a combustion reaction?

A combustion reaction is characterized by a substance combining with oxygen (O₂) to produce energy, usually in the form of heat and light. This process typically involves hydrocarbons or organic compounds reacting with oxygen to yield carbon dioxide (CO₂) and water (H₂O) as byproducts. The release of energy is a hallmark of combustion reactions, making them exothermic; that is, they release more energy than they consume, which is essential for processes such as burning fuels.

In contrast, other options describe different types of reactions. Some reactions may occur without oxygen or may absorb energy, but these do not fit the definition of combustion. Additionally, while gases are often produced during combustion, the presence of solid or liquid reactants or products would contradict the notion that combustion exclusively generates gases. Hence, the correct answer accurately captures the essence of combustion reactions in chemistry.