What type of reaction is represented by the equation A + B → C + D?

The equation A + B → C + D suggests that two reactants, A and B, are combining to form two products, C and D. This is characteristic of a combination reaction, where multiple reactants come together to form a single product or products. In this case, since it involves just two reactants producing multiple products, it aligns well with the notion of a combination reaction.

In contrast, a decomposition reaction involves a single reactant breaking down into two or more products, which is not represented here as there are two separate reactants producing two products. A single replacement reaction typically involves an element in a compound being replaced by another element, which also does not fit this equation. Lastly, a double replacement reaction involves the exchange of ions between two compounds, leading to new products; however, this is not applicable since there are not two distinct compounds undergoing an exchange here.

Thus, the equation showcases the essence of what a combination reaction represents in chemical processes.