Which element is estimated by the Carius method?

The element whose percentage composition in an organic compound can be determined by the Carius method is

In phosphorus estimation,$0.31 \ g$ of an organic compound gave $0.444 \ g$ of magnesium pyrophosphate (molar mass $= 222 \ g \ mol^{-1}$). The percentage of phosphorus in the compound is

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 $Hg$ ]

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

Match Column-$I$ and Column-$II$ with the correct relation:

Column-$I$	Column-$II$
$(i).$ Magnesium pyrophosphate	$(a).$ $I_2O_5$
$(ii).$ Barium sulphate	$(b).$ $AgX$
$(iii).$ Iodide pentoxide	$(c).$ $Mg_2P_2O_7$
$(iv).$ Silver halide	$(d).$ $BaSO_4$