Major product $(A)$ is:

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?

$A$ hydrocarbon with molecular formula $C_4H_6$ undergoes the following reactions:
$A$. Decolourises molecular bromine.
$B$. Reacts with $HBr$.
$C$. Addition of ozone and then cleavage of the ozonide by $Zn / H_2O$ gives the product $C_4H_6O_2$.
Then,the structure of the hydrocarbon is:

What is the major product of the following $E2$ reaction?

Which of the following is among the major products of the reaction of $(E)-3$-methylpent$-2$-ene with $BH_3$ in $THF$ followed by the addition of $H_2O_2/HO^{-}$?

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)