Which reaction results in the formation of a pair of enantiomers?

$A$ dihalogen derivative $X$ of a three-carbon hydrocarbon reacts with alcoholic $KOH$ to give another hydrocarbon,which gives a red precipitate with ammoniacal $Cu_2Cl_2$. Reaction of $X$ with aqueous $KOH$ gives an aldehyde. The compound $X$ is .......

The decreasing order of reactivity of the following compounds towards nucleophilic substitution $(S_{N}2)$ is :

On heating $CHCl_3$ with aqueous $NaOH$,the product is:

Which one of the following is most reactive towards nucleophilic substitution reaction?

When $32.25 \ g$ of ethyl chloride is dehydrohalogenated,it gives $50\%$ yield of alkene. What is the mass of the product in $g$? (Atomic mass of $Cl = 35.5$)