The secondary and tertiary amines cannot be distinguished by which of the following?

What is the major product $\mathrm{P}$ in the following reaction? 

${\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{CH}}_2{\mathrm{NH}}_2\underset{0°\mathrm{C}}{\overset{{\mathrm{NaNO}}_2/\mathrm{HCl}}{\to }}\mathrm{P}$

Which of the following reagents will be used to distinguish between the above?

$\left(\mathrm{i}\right) \mathrm{p}-$Methylaniline
$\left(\mathrm{ii}\right) \mathrm{N},\mathrm{N}-$Dimethylaniline
$\left(\mathrm{iii}\right) \mathrm{N}-$ethylaniline
$\left(\mathrm{iv}\right) \mathrm{N}-$ethyl$-\mathrm{N}-$methylaniline

Amongst the above, the compounds which do not form diazonium salt with ice-cold ${\mathrm{NaNO}}_2$ and $\mathrm{HCl}$ are:

In the following reaction, $\mathrm{A}$is:

$\mathrm{A}\stackrel{{\mathrm{Br}}_2/{\mathrm{H}}_2\mathrm{O}}{\to }\mathrm{B}\stackrel{{\mathrm{NaNO}}_2+\mathrm{HCl}}{\to }\mathrm{C}\underset{{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}}{\overset{\mathrm{Boling}}{\to }}$ Tribromobenzene

Consider the following reaction sequence for a nitrogen-containing organic compound $\mathrm{A}$:

$\mathrm{A}\stackrel{\mathrm{KOBr}}{⟶}\mathrm{B}\underset{ \mathrm{andydride}}{\overset{\mathrm{Acetic}}{\to }}\mathrm{C}$

Then, $\mathrm{A}$ and $\mathrm{C}$ will be