On earth the largest reservoir of nitrogen is

Options

A. the oceans
B. granite rocks
C. the air
D. the soil

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for the largest reservoir of nitrogen on Earth. A reservoir is a place where a particular substance is stored in large quantities.

2. **Identifying Possible Options**: The options provided are oceans, granite rocks, the air, and the soil. We need to evaluate each option to determine which one contains the most nitrogen.

3. **Analyzing Each Option**:
- **Oceans**: While oceans do contain nitrogen in the form of dissolved gases and nutrients, they are not the largest reservoir.
- **Granite Rocks**: Granite rocks may contain some nitrogen in mineral form, but it is not significant compared to other reservoirs.
- **Soil**: Soil contains nitrogen mainly in organic matter and as part of various compounds, but again, it is not the largest reservoir.
- **Air**: The atmosphere is composed of approximately 78% nitrogen by volume. This means that a significant amount of nitrogen is stored in the air.

4. **Conclusion**: After evaluating all the options, it is clear that the air contains the largest reservoir of nitrogen on Earth.

5. **Final Answer**: The largest reservoir of nitrogen on Earth is the air.

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