What file format is primarily used for iOS app distribution?

The correct file format used for iOS app distribution is IPA, which stands for iOS App Store Package. This format is specifically designed for iOS applications and encapsulates the app, including its binary code and resources, making it suitable for installation on iOS devices such as iPhones and iPads.

The IPA file is essential because, unlike other formats, it adheres to the guidelines and requirements enforced by Apple for app distribution, either through the App Store or for private enterprise deployment. This format comes with necessary metadata and permissions that ensure the app can be correctly installed and run on iOS devices.

In contrast, APK files are used for Android applications, EXE files are Windows executable files intended for running applications on Windows operating systems, and DMG files are disk image files used primarily on macOS for software distribution. Each of these formats serves its own platform and purpose, highlighting the specificity of the IPA format for iOS applications.