In Kjeldahl's method of estimation of nitrogen, `K_(2)SO_(4)` acts as:

In Kjeldahl's method of estimation of nitrogen, K_2SO_4 acts as:

In kjeldahl's method of estimation of nitrogen, copper sulphate acts as :

The catalyst used in Kjeldahl's method for the estimation of nitrogen is:

In Kjeldahl's method of estimation of N,CuDO_(4) acts as

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

Briefly explain the principle involved in Kjeldahl's method for the estimation of nitrogen.