Final answer:
The correct server response code when a page does not exist is 404 Not Found. It informs the user that the requested page is not available on the server.
Step-by-step explanation:
The best choice for a server response code if a page doesn't exist is C) 404. This HTTP status code indicates that the server was able to communicate with the client, but the server could not find what was requested. A 404 Not Found error is a standardized HTTP status code that tells the user that the server could not find the requested resource.
HTTP status codes are three-digit numbers returned by a web server in response to a request made by a client (such as a web browser) to indicate the outcome of the request. They are part of the HTTP (Hypertext Transfer Protocol) standard and provide information about the status of the requested resource or action. The status code is included in the response header sent by the server.