Question

it is said that oxgen is essential for burning. where does this oxygen come from?

Answer 1

hey oxygen is present everywhere in our atmosphere as it is inorganic substance

Answer 2

Oxygen for burning comes from air, which is 21% oxygen.
Burning means that a substance reacts with oxygen and in many cases forms a some kind of oxide. So yes, oxygen, in some form, is required. It doesn't have to be pure oxygen though.

hope this helps u