The largest reservoir of nitrogen on earth is:A. SoilB. OceansC. Air D. Granite rocks

The correct answer is C. Air.
1. Nitrogen in the Atmosphere:
o The Earth's atmosphere is the largest reservoir of nitrogen, containing approximately 78% nitrogen gas (N₂) by volume.
o This nitrogen exists in a diatomic form (N₂), which is highly stable and inert, making it unavailable directly to most living organisms.
o The total amount of nitrogen in the atmosphere far exceeds the quantity found in other reservoirs such as soil, oceans, or rocks.
2. Nitrogen in Soil:
o Soil contains nitrogen in the form of organic matter, ammonium (NH₄⁺), nitrites (NO₂⁻), and nitrates (NO₃⁻).
o These forms are critical for plant growth but represent only a small fraction of the Earth's total nitrogen compared to the atmosphere.
3. Nitrogen in Oceans:
o Nitrogen is dissolved in seawater as nitrogen gas (N₂) and other compounds like nitrates and nitrites.
o While the oceans are a significant reservoir for other elements, their nitrogen content is much lower than that of the atmosphere.
4. Nitrogen in Granite Rocks:
o Nitrogen in rocks, including granite, is negligible compared to other reservoirs. Rocks are not a significant source of nitrogen in the nitrogen cycle.
The air (atmosphere) is the largest reservoir of nitrogen on Earth, making the correct answer C. Air.