What file format is used for distributing and installing mobile apps on the Android operating system?

The correct answer is .apk file, as this is the standard file format used for distributing and installing applications on the Android operating system. APK stands for Android Package Kit, and it is the file format that contains all the necessary components needed for an Android application to run on a device. This includes the application's code, resources, assets, certificates, and manifest file.

When a user downloads an app from the Google Play Store or installs an app from another source, they are essentially downloading an APK file. This file is then executed by the Android system to successfully install the application on the user's device.

The other file formats mentioned do not serve this purpose. The .exe file is primarily associated with Windows applications, the .app file is used for macOS applications, and the .zip file is a compression format that can store multiple files but is not specific to application installation in the Android ecosystem.