Which is the weakest base among the following?

The acid strength order is:

Order of ${\mathrm{K}}_{\mathrm{a}}$ which can be predicted by following reaction is:

The gases produced in the following reactions are respectively:

$\mathrm{I}: {\mathrm{CH}}_3{\mathrm{NH}}_2+{\mathrm{NH}}_2\mathrm{Br}\to$

$\mathrm{II}: {\mathrm{CH}}_3{\mathrm{SO}}_3\mathrm{H}+{\mathrm{NaHCO}}_3⟶$

$\mathrm{III}:$ 

Decreasing order of enol content of the following compounds in liquid phase: