Final answer:
The external entity symbol portrays a source or destination of data outside the system in a data flow diagram (DFD).
Step-by-step explanation:
The symbol that portrays a source or destination of data outside the system in a data flow diagram (DFD) is the external entity symbol (option b).
The external entity symbol represents external sources or destinations of data that interact with the system being modeled. It can be used to represent entities such as people, organizations, or other systems that send data into the system or receive data from the system.
For example, in a DFD for an online shopping system, a customer would be represented as an external entity symbol since they are a source of data (such as placing an order) that comes into the system.