The reaction of $HNO_2$ with $A$ gives a quaternary ammonium salt. $A$ is

In the reaction sequence $A$ $\xrightarrow{Sn/HCl} B$ $\xrightarrow{HNO_2, 0^{\circ}C} C$ $\xrightarrow{C_2H_5OH} C_6H_6$,identify the functional groups present in $A, B,$ and $C$.

The reaction of amides with $Br_2$ and $OH^-$ (Hofmann bromamide degradation) involves an intramolecular migration of the alkyl group from the carbonyl carbon to the nitrogen atom with retention of configuration at the migrating center. Predict the products for the following reaction:
(Image shows two substituted cyclohexanecarboxamides reacting with $Br_2/OH^-$)

$CH_3-CH_2-CH(CH_3)-CONH_2$ $\xrightarrow[ \Delta ]{ Br_2/KOH } (A)$ $\xrightarrow[ (2) AgOH/\Delta ]{ (1) CH_3I (excess) } (B)$. The major product $(B)$ is:

If an organic compound is treated with $NaNO_2$ and $HCl$ in the presence of ice and nitrogen gas is evolved,what is the compound?

Isoniazid is used in the treatment of tuberculosis. Identify the least basic $N$ atom present in it.