Question

1. Which are more important?
2. Which are most important?
3. Which is more important?
4. Which are most important?
5. Which is the most important?
6. Which are the most important?

(Which one is correct? Are all OK? What is the difference?)

Answer 1

All of those are ok. When you use the word "is" you are talking about one thing.

When you use "are" then you are talking about more than one.

When you use "More" you care comparing two things.

When you use "most" you are comparing more one thing to many other things.