How many oxygen is on earth?

There is over 50 trillion tons of oxgen

Just one.

There r 5

I think you should use 'much' instead of 'many' as oxygen is uncountable.. Anyway, I do not know the answer.

3.2 is good, but we don't know if there will be more girls than boys cause we can't predict the future. if there are more girls then human population might extinct by 2100 also the adding pollution...