Which is the weakest Bronsted base?

What is the color of the precipitate formed when aniline reacts with $HNO_2$ at low temperature,followed by treatment with an alkaline $\beta$-naphthol solution?

What is formed when benzylamine reacts with nitrous acid?

In the above conversion of compound $(X)$ to product $(Y)$,the sequence of reagents to be used will be:

$A$ hydrocarbon $A$ $(C_{4}H_{8})$ on reaction with $HCl$ gives a compound $B$ $(C_{4}H_{9}Cl)$ which on reaction with $1 \ mol$ of $NH_{3}$ gives compound $C$ $(C_{4}H_{11}N)$. On reacting with $NaNO_{2}$ and $HCl$ followed by treatment with water,compound $C$ yields an optically active compound $D$. The compound $D$ is

Which of the following is the strongest base in an aqueous solution?