Write the names of three processes in which oxygen is used and one process by which it returns to the atmosphere.

(N/A) Three processes in which oxygen is used are:
$1$. Respiration: Living organisms consume oxygen to break down glucose and release energy.
$2$. Combustion: Burning of fuels requires oxygen.
$3$. Formation of oxides: Oxygen reacts with various elements (like metals and non-metals) to form oxides.
The process by which oxygen returns to the atmosphere is:
$1$. Photosynthesis: Green plants release oxygen as a byproduct during the process of food synthesis.