Question

explain briefly how the amount of oxygen in air does not change, inspite of the fact that a large amount of it is used in combustion and respiration?

Answer 1

hi mate here is your ans.

In spite of excessive use of oxygen during respiration and combustion,
oxygen in the air does not get depleted. This is due to a process called
photosynthesis. By this process, plants synthesise food from carbon
dioxide and moisture in presence of sunlight. In this process oxygen is
liberated and goes into the air. Thus, the percentage of oxygen in the
atmosphere remains constant.
hope it will help you.

Answer 2

Oxygen is used for combustion and respiration but we should not forget that when we exhale, we release CO2 .Plants take in carbon dioxide and give out oxygen.Hence,the amount of oxygen remains the same.It slightly changes sometimes.