In which of the following carbocation rearrangement takes place with change in carbon skeleton:

Observe the following reaction sequence.

Which is correct acidic strength order:

Give the stability order of following radicals:

$\left(\mathrm{I}\right) {\mathrm{CH}}_3-\stackrel{\bullet }{\mathrm{C}}{\mathrm{H}}_2$ 

$\left(\mathrm{II}\right) {\mathrm{CH}}_3-\stackrel{\bullet }{\mathrm{C}}\mathrm{H}-{\mathrm{CH}}_3$

$\left(\mathrm{III}\right) {\mathrm{CH}}_2=\mathrm{CH}-\stackrel{\bullet }{\mathrm{C}}\mathrm{H}-{\mathrm{CH}}_3$

$\left(\mathrm{IV}\right)$