Some Questions about APNs

Hi, I'm writing a report about different operating systems for mobile devices as homework for university. Things are going quite good, but there are some questions left over about Apples Push Notifications:

One device gets a unique ID for receiving PNs from the Apple server. Does it really always stay the same for one hardware?

When iOS gets a Push Notification, how does it know which app it is for?

What happens if my device isn't connected to the internet when the Push Notification Server gets the request to send a PN to my device?

I would be very happy if anyone could help me with that.

Thanks!