Restricting applications from communicating directly to each other is an example of what Android security principle:

Application Sandboxing is the correct answer because it isolates applications from each other and from the operating system, preventing them from accessing each other's data or processes without explicit permission. This restriction on inter-app communication is a core tenet of sandboxing. Verified Boot ensures the integrity of the device's software from boot-up. SafetyNet is a set of APIs that assess the security and compatibility of a device. ASLR is a memory protection technique that randomizes memory addresses to make it harder for attackers to predict target addresses. While all are Android security principles, only Application Sandboxing directly addresses the isolation of applications from one another.