In Kjeldahl's method, nitrogen present is estimated as

Options

A. `N_2`
B. `NH_3`
C. `NO_2`
D. none of these

Explanation

### Step-by-Step Solution:

1. **Understanding Kjeldahl's Method**:
- Kjeldahl's method is a technique used to determine the nitrogen content in organic compounds. It is widely used in various fields, including agriculture and food science.

2. **Reaction with Concentrated H2SO4**:
- In the first step of the Kjeldahl method, the organic compound that contains nitrogen is digested with concentrated sulfuric acid (H2SO4). This process converts the nitrogen in the organic compound into ammonium sulfate ((NH4)2SO4).

3. **Formation of Ammonia**:
- The ammonium sulfate formed is then treated with a strong base, typically potassium hydroxide (KOH). This reaction releases ammonia gas (NH3).

4. **Absorption of Ammonia**:
- The ammonia gas produced is then absorbed in a known volume of standard sulfuric acid (H2SO4). This allows for the quantification of nitrogen based on the amount of sulfuric acid neutralized by the ammonia.

5. **Conclusion**:
- The nitrogen present in the organic compound is ultimately estimated as ammonia (NH3) after it is released during the reaction with KOH.

### Final Answer:
- In Kjeldahl's method, nitrogen present is estimated as **ammonia (NH3)**.