Among the following substituted pyridines,the most basic compound is

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:

Decarboxylation of all six possible isomers of diaminobenzoic acids $C_6H_3(NH_2)_2COOH$ yields three products $A, B$ and $C$. Three acids give product $A$,two acids give product $B$ and one acid gives product $C$. The melting point of product $C$ is .....$^{\circ} C$.

In the following sequence of reactions,what is $D$?
$Toluene$ $\xrightarrow{[O]} A$ $\xrightarrow{SOCl_2} B$ $\xrightarrow{NaN_3} C$ $\xrightarrow{Heat} D$

The preferred sites of protonation in the following compounds are:
$(i)$ $CH_3CONHCH_3$
(ii) $2$-aminopyridine

The increasing order of diazotisation of the following compounds is: