Which of the following is considered an open-source operating system?

Windows is a proprietary operating system developed and owned by Microsoft, with its source code not publicly available.

Chrome OS is based on the open-source Chromium OS, but Chrome OS itself, as distributed by Google, contains proprietary components and services.

macOS (formerly Mac OS X) is a proprietary operating system developed by Apple, with its source code not publicly available.

Linux is a widely recognized open-source operating system, meaning its source code is freely available to the public for use, modification, and distribution under licenses like the GNU General Public License. This allows for community-driven development and customization.