Which of the following Nmap commands is used to perform a UDP port scan?

The -sY flag performs an SCTP INIT scan, which targets SCTP ports rather than UDP ports.

The -sS flag performs a TCP SYN half-open stealth scan, which targets TCP ports only and has no effect on UDP.

The -sN flag performs a TCP NULL scan by sending packets with no TCP flags set, which is a TCP-based technique unrelated to UDP.

The -sU flag instructs Nmap to perform a UDP scan by sending UDP packets to target ports and analyzing responses. If no response is received the port is marked open|filtered; an ICMP port unreachable message marks it closed. UDP scanning is slower than TCP scans and requires elevated privileges to execute.