Which of the following compounds gives the smell of mustard oil?

In the below given synthetic sequence,the product "$C$" is

Identify $X$ and $Y$ in the following reactions:

In the series of reactions: $C_6H_5NH_2$ $\xrightarrow{NaNO_2/HCl}_{0 - 5\ ^\circ C} X$ $\xrightarrow{HNO_2}_{H_2O} Y + N_2 + HCl$. $X$ and $Y$ are respectively:

Which of the following compounds does not give alcohol on reduction?

The correct stability order of the following diazonium salts is: