A support question we get here regularly is “How do you quit the app?”
You don’t. Notice that other mobile apps do not have exit buttons. When the user is done, he simply starts another app or the menu. Just like on websites: you don’t exit a website, you just go on to the next one.
Apple’s take on this is if an app quits on its own, it will present as a crash. It will therefore not be accepted into the App Store.