Which of the following operating systems is considered open source?

Android is considered an open-source operating system because its source code is made publicly available for anyone to view, modify, and distribute. This model fosters collaboration and innovation within the development community, allowing developers to adapt the system for their needs or create customized versions. The Android Open Source Project (AOSP) serves as the base for the Android operating system, ensuring that the core elements can be freely accessed and utilized.

In contrast, iOS, Windows, and macOS are proprietary operating systems. Their source codes are owned and controlled by their respective companies (Apple for iOS and macOS, and Microsoft for Windows), and users do not have the same level of access to modify or redistribute the software. This proprietary nature restricts customization and collaboration that is inherently possible with an open-source model like Android’s.