Correct Answer:
B. 80
The correct answer is B: 80. The HTTP (Hypertext Transfer Protocol) protocol, which is the foundation of data communication for the World Wide Web, works on port 80 by default. When you type a web address (e.g., http://www.example.com) into your browser without specifying a port number, your browser automatically attempts to connect to port 80 on the web server to retrieve the webpage. This standardization allows for seamless web browsing.
- A: 21 is incorrect. Port 21 is the default port for FTP (File Transfer Protocol), which is used for transferring files between a client and a server on a computer network. It is not used for HTTP communication.
- C: 25 is incorrect. Port 25 is the default port for SMTP (Simple Mail Transfer Protocol), which is used for sending and receiving email messages between email servers. It is not used for web browsing.
- D: 443 is incorrect. Port 443 is the default port for HTTPS (Hypertext Transfer Protocol Secure). HTTPS is the secure version of HTTP, using SSL/TLS encryption to secure communication over a computer network. While related to web browsing, it is for secure connections, whereas HTTP's default is port 80 for unencrypted communication.