Oxygen is returned to the atmosphere mainly by:

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Burning of fossil fuels

Respiration

Photosynthesis

Fungi

answer is C.

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Detailed Solution

Concept- The importance of oxygen in daily life cannot be overstated. Without oxygen, we would perish. It is found in carbohydrates, proteins, nucleic acids, and lipids, among other biological substances.

{CO}_{2}

is released into the atmosphere as a result of the combustion of fossil fuels. Respiration is the process of breaking down glucose in our bodies, either with or without the use of oxygen, to produce energy. In the water cycle, the process of respiration is utilised.
Photosynthesis is a process that uses light energy to convert

{CO}_{2}

into a natural mixture of starch (sugar). During this operation,

O_{2}

is also expelled. Humans and animals consume oxygen and release carbon dioxide into the atmosphere. Plants use this

{CO}_{2}

for photosynthesis, and as a result, they emit

O_{2}

into the atmosphere. Oxygen is absorbed and returned in this manner.
Fungi are eukaryotic multicellular creatures. They are saprophytes, which means they eat dead organic matter.
As a result, we may conclude that photosynthesis is the primary source of oxygen returned to the atmosphere.
Hence, the correct option is (3).

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