Which of the following amines is most basic in nature in the aqueous phase?

Why is benzene diazonium chloride not stored and is used immediately after its preparation?

Aniline in a set of the following reactions yielded a coloured product $Y$.
Aniline $\xrightarrow[(273-278 \ K)]{NaNO_{2}/HCl} X$ $\xrightarrow{N,N-dimethylaniline} Y$
The structure of $Y$ would be

The increasing order of basicity of the following compounds is:

Identify the major product formed from the following reaction sequence.

Which one of the following compounds undergoes bromination of its aromatic ring (electrophilic aromatic substitution) at the fastest rate?