The major product obtained when this substrate is subjected to $E_2$ reaction under the treatment of potassium $tert$-butoxide is:

$A$ primary alkyl halide $(a)$ with molecular formula $C_{4}H_{9}Br$ reacts with alcoholic $KOH$ to give compound $(b)$. Compound $(b)$ reacts with $HBr$ to give compound $(c)$,which is an isomer of $(a)$. When $(a)$ reacts with sodium metal,it gives compound $(d)$ with molecular formula $C_{8}H_{18}$,which is different from the compound formed when $n$-butyl bromide reacts with sodium. Identify the structural formula of $(a)$ and write the equations for all the reactions.

Which of the following is product $A$ in the above reaction?

The back-side attack on $2$-bromobutane by methoxide $(CH_3O^{-})$ gives the product shown below. Which Fischer projection represents $2$-bromobutane used as the reactant in this reaction?

Toluene reacts with excess of $Cl_2$ in the presence of sunlight to give a product which on hydrolysis followed by reaction with $NaOH$ gives:

The product of the reaction is .....