In which of the following compounds is the Kjeldahl method applicable?

In Kjeldahl's method for estimation of nitrogen,$CuSO_4$ acts as :

Which formula is used in the Kjeldahl method for the estimation of nitrogen?

In Duma's method of estimation of nitrogen,$0.1840 \, g$ of an organic compound gave $30 \, mL$ of nitrogen collected at $287 \, K$ and $758 \, mm$ of $Hg$ pressure. The percentage composition of nitrogen in the compound is $......$ . (Round off to the Nearest Integer). [Given : Aqueous tension at $287 \, K = 14 \, mm$ of $Hg$ ]

$0.259 \ g$ of an organic compound gives $0.350 \ g$ of $BaSO_4$ upon treatment. Calculate the percentage of sulphur in the compound. (Atomic masses: $Ba = 137, S = 32, O = 16$) (in $\%$)

$A$ student has been given $0.314 \ g$ of an organic compound and asked to estimate Sulphur. During the experiment, the student has obtained $0.4813 \ g$ of barium sulphate. The percentage of sulphur present in the compound is . . . . . .
(Given Molar mass in $g \ mol^{-1}$: $S = 32$, $BaSO_4 = 233$) (in $\%$)