Which of the following is the major product obtained in the reaction of isobutylene with hydrogen bromide?

The compound $CH_3-C(CH_3)=CH-CH_3$ on reaction with $NaIO_4$ in the presence of $KMnO_4$ gives:

In the following reaction: $CH_3-C(CH_3)_2-CH=CH_2 \xrightarrow{H_2O/H^{+}} A (\text{Major product}) + B (\text{Minor product})$,the major product $A$ is:

$A$ compound $X$ absorbs $2$ moles of hydrogen and $X$ upon oxidation with $KMnO_4 \mid H^{+}$ gives the products shown below:
$CH_3-CO-CH_3$,$CH_3-COOH$ and $CH_3-CO-CH_2-CH_2-COOH$.
The total number of $\sigma$ bonds present in the compound $X$ is . . . . . .

Glycol on treatment with $PI_3$ mainly gives -

The percentage composition of an organic compound $A$ is: carbon = $85.71 \%$ and hydrogen = $14.29 \%$. Its vapour density is $14$. Consider the following reaction sequence:
$A$ $\xrightarrow{Cl_2/H_2O} B$ $\xrightarrow[(ii) H_3O^+]{(i) KCN/EtOH} C$
Identify $C$.