Mention the three processes in which oxygen is used up from the atmosphere and the only process in which it is returned to the atmosphere.

(N/A) The three processes in which oxygen is consumed from the atmosphere are:
$1$. Combustion (burning of fuels).
$2$. Respiration (by living organisms).
$3$. Formation of oxides (e.g.,rusting of metals).
The only process by which oxygen is returned to the atmosphere is:
$1$. Photosynthesis (carried out by green plants).