Final answer:
The purpose of an event in a BPMN activity diagram is to affect the flow of the business process.
Step-by-step explanation:
The purpose of an event in a Business Process Modeling Notation (BPMN) activity diagram is to affect the flow of the business process. Events are used to trigger actions or conditions that change the flow of the diagram. They can represent the start or end of a process, a change in state, or an external event that influences the process. For example, an event could be used to represent the receipt of an order, which would then trigger the subsequent workflow in the diagram.