What is the purpose of a URL's protocol?

The purpose of a URL's protocol is to specify how to access the resource. It indicates the method used for communication between the client and the server. Common protocols include HTTP, HTTPS, FTP, and others, each designed for different types of data transmission or interaction.

For example, the HTTP protocol is used for transferring web pages, while HTTPS (the secure version of HTTP) provides a secure transmission by implementing encryption, which prevents unauthorized access to the data being sent. This distinction of the protocol sets the stage for how to initiate the actual connection to the desired resource over the Internet, guiding the browser or client software on how to handle the request.

The other choices do not encompass the primary role of the protocol. The domain name is part of the URL that provides the address of the resource, identifying where it resides on the Internet. The file type is not specified by the protocol but rather can be inferred from the file extension or content type. Encryption is a feature related specifically to certain protocols like HTTPS but does not describe the main objective of a URL's protocol itself.