Plant maintains the balance of ......... in the atmosphere.

Photosynthesis is the process in which autotrophs such as green plants use carbon dioxide and water in presence of sunlight to synthesize nutrients such carbohydrates in the form of glucose and release oxygen. Hence oxygen is returned to the atmosphere by photosynthesis. This oxygen from the atmosphere is taken in by animals for carrying out the process of respiration and carbon dioxide is evolved. This carbon dioxide is used by plants and the same cycle continues. Hence plants maintain the balance of oxygen and carbon dioxide in the atmosphere. Thus the correct answer is option C.