Which one of the following has the most nucleophilic nitrogen?

Yellow dye can be prepared by a coupling reaction of benzene diazonium chloride in acidic medium with $X$. Identify $X$ from the following.

$A$. Phenyl methanamine
$B$. $N,N$-Dimethylaniline
$C$. $N$-Methylaniline
$D$. Benzenamine
Choose the correct order of basic nature of the above amines.

Explain the acylation of ethanamine and aniline.

Given below are two statements:
Statement $I$: Primary aliphatic amines react with $HNO_2$ to give unstable diazonium salts.
Statement $II$: Primary aromatic amines react with $HNO_2$ to form diazonium salts which are stable even above $300 \ K$.
In the light of the above statements,choose the most appropriate answer from the options given below:

Identify $B$ in the following reaction: Acetaldoxime $\xrightarrow[\text{alcohol}]{Na} A$ $\xrightarrow[HCl]{NaNO_2} B + H_2O + N_2 \uparrow$