What’s the difference between native, hybrid, and cross-platform apps? Explain the Android Activity (or iOS ViewController) lifecycle. How do you manage data persistence on a mobile device? Describe MVC, MVP or MVVM and how you’ve applied one in an app. What strategies do you use to optimize app performance and battery life? How do you handle memory management and avoid leaks? Explain how you implement background tasks or push notifications. What measures do you take to secure sensitive user data? How do you approach testing (unit, UI, integration) for mobile apps? Tell me about a challenging bug you fixed in a previous mobile-dev project.