Hard what am I riddles with simple answers

what am Itricky

While I am in air, I am not in oxygen. I am also in water, but not in hydrogen. I am necessary in all animals, but you won't find me in the zoo. Look in all brains and you'll find me there too. What am I?
The Letter A.
65.62 %
204 votes
cleanwhat am I

You write on me and secrets I can keep. In places never seen. I spin like a top. Though stiff as a board, I'm often described like a mop. What am I?
A Floppy Disk.
1.50 %
2649 votes
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