What component of earth’s atmosphere exists entirely as a result of photosynthesis?

oxygen gas
water vapor
nitrogen gas
carbon dioxide gas

oxygen gas

An earth's atmosphere consists of layers of gases. All these gases collectively form air. Air consist of oxygen, nitrogen, carbon  dioxide, aerosol and other gases obtain from various vital and non vital processes taking place on earth. Photosynthesis is a process of synthesis of food by the plants which involves carbon dioxide, water and sunlight as reactants and glucose and oxygen gas are liberated as product in the atmosphere. The removal of forests by deforestation on a large scale can limit the oxygen level in the earth's atmosphere.  

Oxygen gas is the component of Earth's atmosphere exists entirely as a result of photosynthesis.

"griffith's experiment discovering the "transforming principle" in pneumococcus bacteria. griffith's experiment, reported in 1928 by frederick griffith, was the first experiment suggesting that bacteria are capable of transferring genetic information through a process known as transformation." - griffith's experiment.