What characterizes a combination reaction?

A combination reaction is characterized by the process in which two or more reactants come together to form a single product. This type of reaction can be represented by a general equation where multiple reactants combine to produce one compound. It reflects the fundamental principle of conservation of mass, as the total mass of the reactants equals the total mass of the product formed.

In a combination reaction, the reactants can be elements or simpler compounds, and the product is typically a more complex compound. This contrasts with other types of reactions, such as decomposition reactions, where a single compound is broken down into simpler substances, or substitution and double displacement reactions, where components of different compounds are exchanged.

This uniqueness makes option B the defining characteristic of combination reactions, as it clearly captures the idea of multiple reactants forming a single product, aligning with the chemical principles that govern these transformations.