Question

what component of earths atmosphere exists entirely as a result of photosynthesis?
oxygen gas
water vapor
nitrogen gas
carbon dioxide gas

Explanation:

Photosynthesis is the process by which plants, algae, and some bacteria use sunlight, carbon - dioxide, and water to produce glucose and oxygen. Oxygen gas is a by - product of photosynthesis and a significant component of Earth's atmosphere that exists largely due to this process. Water vapor is present from evaporation and transpiration, nitrogen gas is abundant in the atmosphere from natural processes not directly related to photosynthesis, and carbon dioxide is taken in by photosynthesis rather than being a product of it in the context of this question.

Answer:

A. oxygen gas