Choose the forms in which most plants absorb nitrogen:1. Proteins 2. Nitrates and nitrites3. Urea 4. Atmospheric nitrogenChoose the correct option.

To determine how most plants absorb nitrogen, we can analyze the given options based on common knowledge of plant nutrition.

1. Proteins: Plants do not directly absorb proteins. Instead, they absorb simpler forms and then synthesize proteins internally.

2. Nitrates and Nitrites: This is the most common form of nitrogen absorption for plants. Nitrates (NO₃⁻) and nitrites (NO₂⁻) are readily taken up by plant roots from the soil.

3. Urea: While some plants can utilize urea, it is less commonly absorbed directly as a nitrogen source compared to nitrates and nitrites.

4. Atmospheric Nitrogen: Atmospheric nitrogen (N₂) is not readily absorbed by most plants directly; instead, certain bacteria and legumes are involved in the nitrogen fixation process that converts it into usable forms like nitrates.

Final Answer

The correct option is 2. Nitrates and nitrites.