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?

In the following reaction
$C_6H_5CH_2Br \xrightarrow[{(ii)H_3O^{+}}]{{(i)Mg, \text{Ether}}} X$
Product $X$ is

On treatment with chlorine in the presence of sunlight,toluene gives the product

Find the reactants which on heating with alcoholic $KOH$ produce the compound $CH_3-CH_2-CH_2-CH=CH_2$.
$(i) \ CH_3-CH(Br)-CH_2-CH_2-CH_3$
$(ii) \ CH_3-CH_2-CH(Br)-CH_2-CH_3$
$(iii) \ CH_3-CH_2-CH_2-CH_2-CH_2Br$
$(iv) \ CH_3-CH_2-CH_2-CH(Br)-CH_3$

The hybridization state of carbon atoms in the product formed by the reaction of ethyl chloride with aqueous potassium hydroxide is

$A$ dihalogen derivative '$X$' of a hydrocarbon with three carbon atoms reacts with alcoholic $KOH$ to give another hydrocarbon which forms a red precipitate with ammoniacal $Cu_2Cl_2$. '$X$' gives an aldehyde upon reaction with aqueous $KOH$. What is the compound '$X$'?