$2-\text{Methylpropan}-2-\text{ol}$ on oxidation under drastic conditions, gives _____ as the final product.

${\mathrm{C}}_{\mathrm{5}}{\mathrm{H}}_{\mathrm{10}}\mathrm{ }\stackrel{\mathrm{A}}{\to }{\mathrm{C}}_{\mathrm{5}}{\mathrm{H}}_{\mathrm{12}}\mathrm{O} \stackrel{\mathrm{B}}{\to } {\mathrm{CH}}_{\mathrm{3}}({\mathrm{CH}}_{\mathrm{2}}{\mathrm{)}}_{\mathrm{2}}\mathrm{COOH};$ $\mathrm{A}$ and $\mathrm{B}$ in the above reactions are ______.

When vapours of an alcohol were passed over hot reduced copper, it gave an olefin. The alcohol is$/$are _______.

The final product $\left(\mathrm{IV}\right)$ in the following sequence of reactions is ______.