Explanation

(c)
Kejldahl’s method is used for the estimation of nitrogen. The organic compound is heated with conc. $H_{2}SO_{4}$ in presence of $K_{2}SO_{4}$ (used to elevate boiling point of $H_{2}SO_{4}$) and $CuSO_{4}$ (used as catalyst) to convert all the nitrogen into $\left( NH_{4} \right)_{2}SO_{4}$.