Azo-dyes are prepared from:

$A$ mixture containing the following four compounds is extracted with $1 \, M \, HCl$. The compound that goes to the aqueous layer is:
$(I)$ Cyclohexyl methyl sulfide
$(II)$ $N$-methylcyclohexylamine
$(III)$ Methoxycyclohexane
$(IV)$ Cyclohexyl methyl ketone

Ethyl amine on heating with $CS_2$ in presence of $HgCl_2$ forms

The major product formed in the following reaction is:

The product $C$ of the following reaction sequence is:

Aniline in a set of reactions yielded a product $D$. The structure of product $D$ would be:
Aniline $\xrightarrow{NaNO_2/HCl} A$ $\xrightarrow{CuCN} B$ $\xrightarrow{H_2/Ni} C$ $\xrightarrow{HNO_2} D$