What are the bond enthalpies and bond lengths between carbon and carbon atoms in alkanes and alkenes?

Consider the following reaction in which the intermediate carbocation loses $H^{+}$ to give the final product:
Which of the following energy profiles best represents the overall reaction?

The product $(Z)$ is:

The octane number can be improved by $...............$.

The products obtained in the above Wurtz reaction are:

The cycloalkane $(X)$ on bromination consumes one mole of bromine per mole of $(X)$ and gives product $(Y)$ in which $C:Br$ ratio is $3:1$. The percentage of bromine in the product $(Y)$ is $ . . . . . . \%$ (Nearest integer).
(Given: Molar mass in $g \ mol^{-1}$, $H:1, C:12, O:16, Br:80$)