The acceptable resonating structure(s) of the following molecule is/are:

Arrange the following compounds in order of decreasing acidity.

What is the order of stability of the following carbocations ?

$\left(\mathrm{I}\right) {\mathrm{CH}}_2=\mathrm{CH}-\stackrel{\oplus }{\mathrm{C}}{\mathrm{H}}_2$  $\left(\mathrm{II}\right) {\mathrm{CH}}_3-\stackrel{\oplus }{\mathrm{C}}{\mathrm{H}}_2;$ $\left(\mathrm{III}\right)$