Question

why does a percentage of gases like oxygen,nitrogen and carbon dioxide remain almost same in the atmosphere?

Answer 1

no.
oxygen:- 21%
nitrogen:- 78%
co2 :- 0.03%

there is a huge difference btw these gases
■how can u say that they are present approx in same amount??

Answer 2

$\sf\huge{\rm{Answer-}}$

Oxygen, nitrogen and carbon dioxide continue to cycle through gaseous cycles between abiotic and biotic components of the environment. Their composition is, therefore, being maintained.