Which of the following command line switch would you use for OS detection in Nmap?

-D enables decoy scanning, which spoofs multiple source IP addresses to obscure the true scanner identity, not OS detection.

The -O flag in Nmap enables operating system detection by sending a series of TCP and UDP probes to the target and comparing responses against a database of known OS fingerprints. This allows the scanner to make educated guesses about the target's operating system, version, and device type. It is the standard and well-documented switch for OS detection in Nmap.

-P flags (such as -Pn, -PS, -PA) control host discovery and ping behavior, not operating system fingerprinting.

-X is not a recognized standard Nmap command-line switch and has no defined function in Nmap.