The product $(A)$ is

Which of the following products cannot be obtained in the above reaction?

Which series of reactions will achieve the following transformation?

The major product $'A'$ of the following given reaction has $......\,sp^2$ hybridized carbon atoms.
$2,7-\text{Dimethyl}-2,6-\text{octadiene} \xrightarrow{H^{+}} A \text{ (Major Product)}$

Which is the most precise designation of stereochemistry for the products formed in the electrophilic addition of $DBr$ to $1$-methylcyclohexene? ($D = {}^2H$,an isotope of hydrogen)

Provide the bond lengths for hydrogen, ethane, ethene, and ethyne.