Most common form of nitrogen uptake and usable forms for plants are respectively.

Options

A. `NO_3^(-), NO _ 2 ^(-) `
B. ` N H _ 3 , NO_(3) ^(-) `
C. ` NO _ (3) ^(- ), NH _ 3 `
D. ` NH_ 3 , NO _ 2 ^( - ) `

Answer

To answer the question regarding the most common form of nitrogen uptake and the usable forms for plants, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding Nitrogen in the Atmosphere**:
- Nitrogen is abundant in the atmosphere, primarily in the form of N₂ gas. However, plants cannot directly utilize atmospheric nitrogen.

**Hint**: Remember that atmospheric nitrogen (N₂) needs to be converted into a usable form for plants.

2. **Nitrogen Fixation**:
- Atmospheric nitrogen is converted into ammonia (NH₃) through a process called nitrogen fixation. This process is facilitated by certain bacteria, such as Rhizobium, which live in the root nodules of legumes.

**Hint**: Identify the role of bacteria in converting N₂ to NH₃.

3. **Nitrification**:
- The ammonia produced can be further converted into nitrites (NO₂⁻) and then into nitrates (NO₃⁻) through a process known as nitrification. This conversion is carried out by specific bacteria, including Nitrosomonas (which converts ammonia to nitrite) and Nitrobacter (which converts nitrite to nitrate).

**Hint**: Focus on the two-step process of nitrification and the specific bacteria involved.

4. **Uptake by Plants**:
- Plants primarily absorb nitrogen in the form of nitrate (NO₃⁻) from the soil. Nitrate is the most common form of nitrogen that plants take up.

**Hint**: Recall which form of nitrogen is absorbed by plants from the soil.

5. **Assimilation**:
- Once inside the plant, nitrate is reduced to ammonia, which is then used to synthesize amino acids. This process of converting inorganic nitrogen into organic molecules is known as assimilation.

**Hint**: Understand the transformation of nitrate into ammonia within the plant.

6. **Conclusion**:
- Therefore, the most common form of nitrogen uptake by plants is nitrate (NO₃⁻), and the usable form of nitrogen for plants is ammonia (NH₃).

### Final Answer:
The most common form of nitrogen uptake by plants is **nitrate (NO₃⁻)**, and the usable form for plants is **ammonia (NH₃)**.