How is the percentage of oxygen determined in the quantitative estimation of organic compounds?

The Kjeldahl method of nitrogen estimation fails for which of the following reaction products $?$
$(a)$ Nitrobenzene $\xrightarrow{Sn/HCl}$ Aniline
$(b)$ Benzonitrile $\xrightarrow{LiAlH_4}$ Benzylamine
$(c)$ Benzyl cyanide $\xrightarrow{(i) SnCl_2 + HCl, (ii) H_2O}$ Phenylacetaldehyde
$(d)$ Aniline $\xrightarrow{NaNO_2/HCl}$ Benzenediazonium chloride

Which element is estimated by the Carius method?

In the Carius method for the estimation of halogens,$0.15 \, g$ of an organic compound gave $0.12 \, g$ of $AgBr$. Find the percentage of bromine in the compound. (in $\%$)

In the Kjeldahl's method for estimation of nitrogen present in a soil sample,ammonia evolved from $0.75 \ g$ of sample neutralized $10 \ mL$ of $1 \ M \ H_2SO_4$. The percentage of nitrogen in the soil is (in $.33$)

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 $\%$)