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

In the estimation of sulphur in an organic compound,upon treatment with concentrated $HNO_3$,it is converted into:

In Carius method for estimation of halogens,$0.2 \, g$ of an organic compound gave $0.188 \, g$ of $AgBr$. The percentage of bromine in the compound is $......$ . (Nearest integer)
[Atomic mass: $Ag=108, Br=80$ ]

Describe the Kjeldahl's method and the principles for the estimation of nitrogen present in an organic compound.

Given below are two statements $I$ and $II.$
Statement $I :$ Dumas method is used for estimation of Nitrogen in an organic compound.
Statement $II :$ Dumas method involves the formation of ammonium sulphate by heating the organic compound with conc $H_2SO_4$. In the light of the above statements,choose the correct answer from the options given below.

$0.3780 \, g$ of an organic chloro compound gave $0.5740 \, g$ of silver chloride in Carius estimation. Calculate the percentage of chlorine present in the compound. (in $\%$)