Decreasing the concentration of an electrophile (substrate) in a typical $S_N2$ reaction by a factor of $3$ will cause the reaction rate to

Which of the following procedures would be best for achieving the following reaction?

Ethyl bromide gives ethylene when reacted with

The major product in the reaction is:

In the following reactions,
$(i) CH_3-CH(CH_3)-CH(OH)-CH_3 \xrightarrow{H^{+}/\text{heat}} A \text{ [Major product]} + B \text{ [Minor product]}$
$(ii) A$ $\xrightarrow[\text{in absence of peroxide}]{HBr, \text{dark}} C \text{ [Major product]} + D \text{ [Minor product]}$
the major products $(A)$ and $(C)$ are respectively:

$A$ 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 '$X$'?