During the quantitative estimation of $C$ and $H$,the $CO_2$ produced is absorbed in which of the following?

What is the reason for passing dry air through the combustion tube during the estimation of $C$ and $H$?

In sulphur estimation,$0.471 \ g$ of an organic compound gave $1.4439 \ g$ of barium sulphate. The percentage of sulphur in the compound is $.............$ (Nearest Integer) (Given: Atomic mass $Ba: 137 \ u, S: 32 \ u, O: 16 \ u$)

In Dumas' method of estimation of nitrogen,$0.35 \ g$ of an organic compound gave $55 \ mL$ of nitrogen collected at $300 \ K$ temperature and $715 \ mm$ pressure. The percentage composition of nitrogen in the compound would be (aqueous tension at $300 \ K = 15 \ mm$). (in $\%$)

$0.8 \ g$ of an organic compound was analysed by Kjeldahl's method for the estimation of nitrogen. If the percentage of nitrogen in the compound was found to be $42 \ \%$,then $.... \ mL$ of $1 \ M$ $H_2SO_4$ would have been neutralized by the ammonia evolved during the analysis.

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	$(d).$ $BaSO_4$