A combination reaction is a type of chemical reaction where two or more substances combine to form a single product. This process can involve elements or compounds, and it typically releases energy in the form of heat or light. An example of a combination reaction is when hydrogen gas H₂ reacts with oxygen gas O₂ to form water H₂O. These reactions are fundamental in chemistry and are often represented by the general equation: A + B → AB, where A and B are the reactants and AB is the product. Combination reactions are essential in various applications, including industrial processes and biological systems.