Answer:
I help engines spin and pants stay up
I am the ultimate killing machine used not once but TWICE I can be made by humans.
What's 3/7 chicken, 2/3 cat, and 2/4 goat?
I am lighter than air, but a hundred people cannot lift me. Careful, I am fragile. What am I?
What can you lose that will cause other people to lose theirs too?
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?