Question

why we can't increase the amount of oxygen in atmosphere as it can be prepared by different methods?

Answer 1

its simple because it wiil require millions of rupees and who wants to spend such amount of money?? More than that you must understand that earth is very large than you think so If we start to increase the amount of oxygen we may be able to increase 1 or 2 percent after huge expenditure and great depletion of resources. But the plants do it for free so, who cares.