In the estimation of nitrogen by Kjeldahl's method 2.8 gm of an organic compound required 20 millimole of `H_2SO_4` for the complete neutralisation of `NH_3` gas evolved. The percentage of nitrogen in the sample is:

Options

A. `20%`
B. `10%`
C. `40%`
D. `30%`

Explanation

To solve the problem of estimating the percentage of nitrogen in the organic compound using Kjeldahl's method, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Given Data:**
- Mass of the organic compound (W) = 2.8 g
- Millimoles of H₂SO₄ used = 20 mmoles

2. **Determine the n-factor for H₂SO₄:**
- In the reaction between H₂SO₄ and NH₃, sulfuric acid dissociates to provide 2 H⁺ ions. Therefore, the n-factor of H₂SO₄ is 2.

3. **Calculate the Milliequivalents of H₂SO₄:**
- Milliequivalents (meq) = Millimoles × n-factor
- Milliequivalents of H₂SO₄ = 20 mmoles × 2 = 40 meq

4. **Use the Formula for Percentage of Nitrogen:**
- The formula for calculating the percentage of nitrogen (N) in the organic compound is:
\[ \text{Percentage of N} = \frac{1.4 \times \text{milliequivalents of H₂SO₄}}{\text{W compound}} \times 100 \]
- Substitute the values into the formula:
\[ \text{Percentage of N} = \frac{1.4 \times 40}{2.8} \times 100 \]

5. **Perform the Calculation:**
- Calculate the numerator: \( 1.4 \times 40 = 56 \)
- Now divide by the weight of the organic compound:
\[ \frac{56}{2.8} = 20 \]
- Thus, the percentage of nitrogen is:
\[ \text{Percentage of N} = 20\% \]

6. **Conclusion:**
- The percentage of nitrogen in the sample is **20%**.