During the estimation of nitrogen present in an organic compound by the Kjeldahl method,the ammonia evolved from $0.5 \ g$ of the compound neutralized $10 \ mL$ of $1 \ M$ $H_{2}SO_{4}$. Find the percentage of nitrogen in the compound. (in $\%$)

$2.18 \ g$ of an organic compound containing sulphur produces $0.12 \ g$ of $BaSO_4$. The percentage of sulphur in the compound is?

$0.25 \ g$ of an organic compound $A$ containing carbon, hydrogen, and oxygen was analysed using the combustion method. The increase in mass of the $CaCl_2$ tube and the potash bulb at the end of the experiment was found to be $0.15 \ g$ and $0.1837 \ g$, respectively. The percentage of oxygen in compound $A$ is $.... \%$. (Nearest integer)
(Given: molar mass in $g \ mol^{-1}$, $H: 1, C: 12, O: 16$)

In the Dumas method,$1 \ g$ of an organic compound gives $50 \ mL$ of $N_2$ gas at $300 \ K$ and $740 \ mm \ Hg$ pressure. If the aqueous tension at $300 \ K$ is $15 \ mm \ Hg$,what is the percentage of nitrogen in the compound?

In an estimation of sulphur by Carius method, $0.2 \text{ g}$ of the substance gave $0.6 \text{ g}$ of $BaSO_4$. The percentage of sulphur in the substance is . . . . . . %. (Given molar mass in $\text{g mol}^{-1}$: $S = 32$, $BaSO_4 = 233$)

Explain the principle of estimation of oxygen in an organic compound.