Final answer:
The port number used to serve requests by DNS is 53.
Step-by-step explanation:
The port number used to serve requests by DNS is 53.
DNS stands for Domain Name System and it is responsible for translating domain names into IP addresses. When a client sends a DNS request, it uses port number 53 to communicate with the DNS server.
For example, when you type a website URL into your browser, the DNS server translates that domain name into an IP address using port number 53 to respond back to your browser with the correct IP address so that it can connect to the server hosting the website.