List question

I am trying to fillet two closed curves. I tried to union them first and fillet them. However problem I am having I have a lot of two sets of closed curves.
I have 2 questions.

1. How do I list from {0,1,2,3,4,5,6,7,8,9} to {{0,1},{2,3},{4,5},{6,7},{8,9}}?
2. How do I list from two of {0,1,2,3,4,5,6,7,8,9} to {{0,0},{1,1},{2,2},{3,3},{4,4},{5,5},{6,6},{7,7},{8,8},{9,9}}?