In Kjeldahl's method of estimation of nitrogen, nitrogen is quantitatively converted to ammonium sulphate. It is then treated with standard solution of alkli. The nitrogen which is present is estimated as

Options

A. `N_(2)` gas
B. `NO_(2)` gas
C. `NH_(3)` gas
D. `(NH_(4))_(2)SO_(4)` ppt

Explanation

To solve the question regarding Kjeldahl's method of estimation of nitrogen, we can break down the process step by step:

### Step-by-Step Solution:

1. **Understanding Kjeldahl's Method**:
- Kjeldahl's method is a widely used technique for determining the nitrogen content in organic compounds. The process involves converting nitrogen into a measurable form.

2. **Conversion to Ammonium Sulfate**:
- In the first step, the organic compound containing nitrogen is digested with concentrated sulfuric acid (H2SO4). During this digestion, nitrogen is converted into ammonium sulfate (NH4)2SO4.

3. **Treatment with Alkali**:
- After the digestion process, the resulting ammonium sulfate is treated with a standard solution of an alkali, typically potassium hydroxide (KOH). This step is crucial as it facilitates the release of ammonia (NH3) from the ammonium sulfate.

4. **Liberation of Ammonia**:
- The reaction between ammonium sulfate and the alkali results in the liberation of ammonia gas (NH3). The reaction can be summarized as:
\[ (NH_4)_2SO_4 + 2 KOH \rightarrow 2 NH_3 + K_2SO_4 + 2 H_2O \]

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

6. **Estimation of Nitrogen**:
- The amount of ammonia absorbed is then titrated with a standard acid, and from this titration, the nitrogen content in the original sample can be calculated.

### Final Answer:
- The nitrogen which is present is estimated as **ammonia gas (NH3)**.