While estimating the nitrogen present in an organic compound by Kjeldahl's method, the ammonia evolved…

The equivalent of ammonia contains 14 grams of nitrogen. The number of equivalents of acid used is equal to number of equivalents of ammonia evolved.

Number of equivalents of acid used $=\mathrm{Normality} \times \mathrm{Volume} \mathrm{in} \mathrm{L}$

Hence, the percentage of nitrogen can be calculated form the following 

$\%\mathrm{N}=\frac{1.4\left({ \mathrm{N}}_1{\mathrm{V}}_1\right)}{ \mathrm{mass} \mathrm{of} \mathrm{organic} \mathrm{compound} }$

$\% \mathrm{N}=\frac{1.4\left(2.5\times 2\times 2\right)}{0.25}=56$