Which one of the following is not a Client-Server application ?

Answer: Ping is not a client-server application.

Reason: A client-server application involves an application-layer client that sends requests to a server which provides services or resources. Ping operates differently.

• Internet chat — typically client-server: chat clients connect to servers that relay messages, manage presence, and store history.

• Web browser — a client that requests resources from web servers (HTTP/HTTPS), following the client-server model.

• E-mail — uses client-server protocols (SMTP for sending, IMAP/POP for retrieval); mail servers store and forward messages.

• Ping — uses ICMP echo request/reply at the network layer as a diagnostic tool between hosts. It is not an application-layer client requesting services from a server.

Therefore, Ping is the correct choice because it is a network utility/protocol rather than a client-server application.