Oxygen is returned to the atmosphere mainly by

Options

A. burning of fossil fuel
B. respiration
C. photosynthesis
D. fungi

Explanation

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about the process through which oxygen is returned to the atmosphere.

2. **Analyzing Option A - Burning of Fossil Fuels**:
- When fossil fuels are burned, they undergo a chemical reaction called combustion.
- During combustion, oxygen is consumed to produce carbon dioxide and energy.
- Therefore, this process does not return oxygen to the atmosphere.

3. **Analyzing Option B - Respiration**:
- Respiration is a biological process where glucose is broken down in the presence of oxygen.
- This process produces carbon dioxide, water, and energy.
- Similar to combustion, oxygen is consumed in respiration, meaning it does not return oxygen to the atmosphere.

4. **Analyzing Option C - Photosynthesis**:
- Photosynthesis is the process by which plants use sunlight, carbon dioxide, and water to produce glucose.
- In this process, oxygen is released as a byproduct.
- Therefore, photosynthesis is the process that returns oxygen to the atmosphere.

5. **Conclusion**: After analyzing all the options, it is clear that the correct answer is **Option C - Photosynthesis**, as it is the only process that releases oxygen back into the atmosphere.