An isocyanide on hydrolysis gives

$A$ compound of molecular weight $180$ is acetylated to give a compound of molecular weight $390$. The number of amino groups in the initial compound is:

How many structural isomers of amine are possible for the molecular formula $C_3H_9N$?

Consider the following four compounds $I, II, III,$ and $IV$.
Choose the correct statement$(s)$.
$(A)$ The order of basicity is $II > I > III > IV$.
$(B)$ The magnitude of $pK_b$ difference between $I$ and $II$ is more than that between $III$ and $IV$.
$(C)$ Resonance effect is more in $III$ than in $IV$.
$(D)$ Steric effect makes compound $IV$ more basic than $III$.

Identify $A$ and $B$ in the following reactions:

Which among the following amines has the lowest $pK_{b}$ value?