Hi,
6. All the students ....... Is All students possible?
If you are talking generally about all the students in the world, don't use 'the'.
Use 'the' if you are talking about specific students, eg all the students in the room, all the students in this university, all the students who are studying French. You also say 'the' if there are two groupsof peoplein the room, teachers and students, and you want to specify 'all the students' as opposed to 'all the teachers'.
It's the same for your other examples.
Best wishes, Clive