What characterizes a single replacement reaction?

A single replacement reaction is characterized by an element reacting with a compound, resulting in the replacement of one component of that compound by the element. This can be summarized by the general form:

[ A + BC \rightarrow AC + B ]

In this reaction, element A displaces element B in the compound BC, forming a new compound AC and leaving B free. The fundamental aspect of a single replacement reaction is this active displacement of one element by another, which distinguishes it from other types of reactions.

For instance, when zinc reacts with hydrochloric acid, zinc displaces hydrogen from the acid, resulting in the formation of zinc chloride and the release of hydrogen gas. This clear exchange reflects the nature of single replacement reactions.

The other options represent different types of reactions: the first describes a double replacement reaction where two ionic compounds participate, the second outlines a decomposition reaction where a single compound breaks down, and the last refers to a synthesis or combination reaction where two elements form a new compound. Each of these types employs distinct mechanisms and characteristics that set them apart from a single replacement reaction.