Which method is used for the estimation of nitrogen in an organic compound?

Describe the principle and reactions involved in the estimation of oxygen in an organic compound.

In the estimation of nitrogen by Kjeldahl's method,$2.8 \ g$ of an organic compound required $20 \ mmol$ of $H_2SO_4$ for the complete neutralisation of $NH_3$ gas evolved. The percentage of nitrogen in the sample is?........$\%$

In the Dumas method for the estimation of nitrogen,$0.388 \ g$ of an organic compound yielded $1.31 \ mL$ of $N_2$ gas collected at $293 \ K$ temperature and $746 \ mm$ pressure. Calculate the percentage of nitrogen in the compound. (Aqueous tension at $293 \ K = 6 \ mm$). (in $\%$)

Fill in the blanks:
$(1)$ ........... solution is added to produce the precipitate of $BaSO_4$ in the estimation of sulphur.
$(2)$ .......... and .... precipitate will be produced by the estimation of phosphorus.
$(3)$ How many elements are estimated in organic compounds?
$(4)$ ......... gas is produced in the Dumas method,but ....... gas is produced in the Kjeldahl's method.

In the estimation of bromine,$0.5 \ g$ of an organic compound gave $0.40 \ g$ of silver bromide. The percentage of bromine in the given compound is $..... \ \%$ (nearest integer).
(Relative atomic masses of $Ag$ and $Br$ are $108 \ u$ and $80 \ u$,respectively).