Question

oxygen is not 78% and nitrogen is not 21%why?

Answer 1

Dear student,
air is a mixture of many gases like Oxygen , nitrogen, helium, neon etc. And many more compounds of these elements . As nitrogen as an element is half-filled and is stable so it not increase its contents in the atmosphere may cause immense pressure or suffocating atmosphere that is not able to breath
Where as Oxygen is exhaled by plants and inhaled by humans so increase in the contents of Oxygen is very harmful for breathing so the right proportion or balanced ratio of these gaese is a indication for as healthy atmosphere.
Regards