Which of the following is an Open Source Operating System?

Answer: Linux is an open-source operating system. Its source code is freely available for viewing, modification, and redistribution (for example, the Linux kernel is licensed under the GPL). Microsoft Windows and macOS are proprietary operating systems; their source code is closed and not available for public modification or redistribution. UNIX denotes a family of operating systems. Many commercial UNIX implementations are proprietary, but there are open-source UNIX-like systems such as FreeBSD, OpenBSD, and NetBSD which are separate projects.