Most of the mass of organic material of a plant comes from

Options

A. water
B. atmospheric oxygen
C. carbon dioxide
D. nitrogen

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about the source of most of the mass of organic material in plants. This refers to the components that contribute to the biomass of the plant.

2. **Identifying the Options**: The options provided are:
- Water
- Atmospheric Oxygen
- Carbon Dioxide
- Nitrogen

3. **Analyzing Each Option**:
- **Water**: While water is essential for plant growth and is involved in photosynthesis, it does not contribute significantly to the mass of organic material.
- **Atmospheric Oxygen**: Plants release oxygen as a byproduct of photosynthesis but do not use it as a source for building organic material.
- **Carbon Dioxide**: This is a key component in photosynthesis. Plants take in carbon dioxide from the atmosphere through their stomata and use it to synthesize glucose, which is a primary organic compound.
- **Nitrogen**: Although nitrogen is vital for plant growth and is absorbed from the soil, it primarily contributes to the formation of amino acids and proteins, not the bulk of organic mass.

4. **Conclusion**: The most significant source of the mass of organic material in plants is carbon dioxide. During photosynthesis, carbon dioxide is converted into glucose, which forms the basis of organic matter in plants.

5. **Final Answer**: Therefore, the correct answer is **Carbon Dioxide**.